Auto merge of #3073 - pnkfelix:clarify-lib.name-in-Cargo.toml, r=alexcrichton

doc fix: clarify lib.name property

doc fix: clarify lib.name property

`extern crate` uses `lib.name`; default is post '-' => '_' substitution.

Author: bors

src/doc/manifest.md

@@ -484,7 +484,9 @@ specified.
 
 [lib]
 # The name of a target is the name of the library that will be generated. This
-# is defaulted to the name of the package or project.
+# is defaulted to the name of the package or project, with any dashes replaced
+# with underscores. (Rust `extern crate` declarations reference this name;
+# therefore the value must be a valid Rust identifier to be usable.)
 name = "foo"
 
 # This field points at where the crate is located, relative to the `Cargo.toml`.