Address requested changes to quickchecking crate.

- Remove `whitelistable` and `blacklistable` types.
- Rename test crate directory from `property_test` to `quickchecking`.
- Add new CI job that checks that this crate continues to build.
- Revise matching logic to be more idomatic.
- Phase out modular arithmetic in favor of `gen_range`.
- Incorporate `unreachable!` into match statements.
- Revise logic for accessing random element of vector, favor `choose`
  over `nth`.
- Proper punctuation and capitalization in comments.
- Using actual structures rather than converting everything to strings
  in order to leverage type system.
- Add `#![deny(missing_docs)]` and filled in documentation required for
  the project to build again.
- Add special case logic so we don't generate structs with `long double`
  fields as it will cause tests to fail unitl issue \#550 is resolved

Note on making sure we don't lose test cases we're interested in
preserving:
We're copying the directories `TempDir` makes so we get things like
this:
```
├── bindgen_prop.1WYe3F5HZU1c
│   └── prop_test.h
├── bindgen_prop.H4SLI1JX0jd8
│   └── prop_test.h
```
I'm not sure that `TempDir` makes any claims about uniqueness, so
collisions
probably aren't impossible. I'm up for any suggestions on a more
bulletproof
solution.

_Tasks not addressed by this PR:_
* TODO: Add `cargo features` logic to allow generating problematic code.
* TODO: Make a [bin] target with CLI to manage test settings.
* TODO: Whitelisting and opaque types.
* TODO: Generate bitfields, C++, I-bogus-codegen cases.

Figured this would be a good point to update the PR but if any of the
above TODO
items should be incorporated before moving forward I'm up for it!

Thanks for taking another look!

r? @fitzgen

Author: shnewto

.travis.yml

@@ -38,6 +38,7 @@ env:
     - LLVM_VERSION="4.0.0" BINDGEN_JOB="expectations" BINDGEN_PROFILE=
     - LLVM_VERSION="4.0.0" BINDGEN_JOB="expectations" BINDGEN_PROFILE="--release"
     - LLVM_VERSION="4.0.0" BINDGEN_JOB="misc"
+    - LLVM_VERSION="4.0.0" BINDGEN_JOB="quickchecking"
 
 matrix:
   fast_finish: true

ci/script.sh

@@ -38,6 +38,11 @@ case "$BINDGEN_JOB" in
         # ./ci/assert-rustfmt.sh
         ;;
 
+    "quickchecking")
+        cd ./tests/quickchecking
+        # TODO: Actually run quickchecks once `bindgen` is reliable enough.
+        cargo check
+        ;;
     *)
         echo "Error! Unknown \$BINDGEN_JOB: '$BINDGEN_JOB'"
         exit 1