Adding new examples and example test runner

src/examples/README.md

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+# AWS Encryption SDK Examples
+
+This section features examples that show you
+how to use the AWS Encryption SDK.
+We demonstrate how to use the encryption and decryption APIs
+and how to set up some common configuration patterns.
+
+## APIs
+
+The AWS Encryption SDK provides two high-level APIs:
+one-step APIs that process the entire operation in memory
+and streaming APIs.
+
+You can find examples that demonstrate these APIs
+in the [`examples`](./java/com/amazonaws/crypto/examples) directory.
+
+## Configuration
+
+To use the library APIs,
+you need to describe how you want the library to protect your data keys.
+You can do this using
+[keyrings](#keyrings) or [cryptographic materials managers](#cryptographic-materials-managers),
+or using [master key providers](#master-key-providers).
+These examples will show you how to use the configuration tools that we include for you 
+as well as how to create some of your own.
+We start with AWS KMS examples, then show how to use other wrapping keys.
+
+* Using AWS Key Management Service (AWS KMS)
+    * How to use a single AWS KMS CMK
+        * [with keyrings](./java/com/amazonaws/crypto/examples/keyring/awskms/SingleCmk.java)
+    * How to use multiple AWS KMS CMKs in different regions
+        * [with keyrings](./java/com/amazonaws/crypto/examples/keyring/awskms/MultipleRegions.java)
+    * How to decrypt when you don't know the CMK
+        * [with keyrings](./java/com/amazonaws/crypto/examples/keyring/awskms/DiscoveryDecrypt.java)
+    * How to decrypt within a region
+        * [with keyrings](./java/com/amazonaws/crypto/examples/keyring/awskms/DiscoveryDecryptInRegionOnly.java)
+    * How to decrypt with a preferred region but failover to others
+        * [with keyrings](./java/com/amazonaws/crypto/examples/keyring/awskms/DiscoveryDecryptWithPreferredRegions.java)
+* Using raw wrapping keys
+    * How to use a raw AES wrapping key
+        * [with keyrings](./java/com/amazonaws/crypto/examples/keyring/rawaes/RawAes.java)
+    * How to use a raw RSA wrapping key
+        * [with keyrings](./java/com/amazonaws/crypto/examples/keyring/rawrsa/RawRsa.java)
+    * How to encrypt with a raw RSA public key wrapping key without access to the private key
+        * [with keyrings](./java/com/amazonaws/crypto/examples/keyring/rawrsa/PublicPrivateKeySeparate.java)
+    * How to use a raw RSA wrapping key when the key is DER encoded
+        * [with keyrings](./java/com/amazonaws/crypto/examples/keyring/rawrsa/RawRsaDerEncoded.java)
+* Combining wrapping keys
+    * How to combine AWS KMS with an offline escrow key
+        * [with keyrings](./java/com/amazonaws/crypto/examples/keyring/multi/AwsKmsWithEscrow.java)
+
+### Keyrings
+
+Keyrings are the most common way for you to configure the AWS Encryption SDK.
+They determine how the AWS Encryption SDK protects your data.
+You can find these examples in ['examples/keyring`](./java/com/amazonaws/crypto/examples/keyring).
+
+### Cryptographic Materials Managers
+
+Keyrings define how your data keys are protected,
+but there is more going on here than just protecting data keys.
+
+Cryptographic materials managers give you higher-level controls
+over how the AWS Encryption SDK protects your data.
+This can include things like
+enforcing the use of certain algorithm suites or encryption context settings,
+reusing data keys across messages,
+or changing how you interact with keyrings.
+You can find these examples in
+[`examples/crypto_materials_manager`](./java/com/amazonaws/crypto/examples/cryptomaterialsmanager).
+
+### Master Key Providers
+
+Before there were keyrings, there were master key providers.
+Master key providers were the original configuration structure
+that we provided for defining how you want to protect your data keys.
+Keyrings provide a simpler experience and often more powerful configuration options,
+but if you need to use master key providers,
+need help migrating from master key providers to keyrings,
+or simply want to see the difference between these configuration experiences,
+you can find these examples in [`examples/masterkeyprovider`](./java/com/amazonaws/crypto/examples/masterkeyprovider).
+
+## Legacy
+
+This section includes older examples,
+including examples of using master keys and master key providers.
+You can use them as a reference,
+but we recommend looking at the newer examples, which explain the preferred ways of using this library.
+You can find these examples in [`examples/legacy`](./java/com/amazonaws/crypto/examples/legacy).
+
+# Writing Examples
+
+If you want to contribute a new example, that's awesome!
+To make sure that your example is tested in our CI,
+please make sure that it meets the following requirements:
+
+1. The example MUST be a distinct class in the [`examples`](./java/com/amazonaws/crypto/examples) directory.
+1. Each example file MUST contain exactly one example.
+1. Each example file MUST contain a static method called `run` that runs the example.
+1. If your `run` method needs any of the following inputs,
+    the parameters MUST have the following types:
+    * `com.amazonaws.encryptionsdk.kms.AwsKmsCmkId` : A single AWS KMS CMK ARN.
+        * NOTE: You can assume that automatically discovered credentials have
+            `kms:GenerateDataKey`, `kms:Encrypt`, and `kms:Decrypt` permissions on this CMK.
+    * `List<com.amazonaws.encryptionsdk.kms.AwsKmsCmkId>` :
+        A list of AWS KMS CMK ARNs to use for encrypting and decrypting data keys.
+        * NOTE: You can assume that automatically discovered credentials have
+            `kms:Encrypt` and `kms:Decrypt` permissions on these CMKs.
+    * `byte[]` : Plaintext data to encrypt.
+    * `java.io.File` : A path to a file containing plaintext to encrypt.
+        * NOTE: You can assume that you have write access to the parent directory
+            and that anything you do in that directory will be cleaned up
+            by our test runners.
+1. Any additional parameters MUST be optional and nullable and not of the same type as the above parameters.