Accept @Header annotation values that are objects

toString is called on the supplied values, then used.

I included this in one of my projects that was failing, and it worked as intended.

Felt like there should've been a more end-to-end test that I could've included here, but I didn't easily see it, and I'm a bit short on time, so point it out if you feel like that needs to be added as well.
Merge pull request #576 from LukeStClair/master

Accept @Header annotation values that are objects
Add a new log level: HEADERS_AND_ARGS
Add @Override annotations
Merge pull request #577 from square/rice/log_headers_and_args

Add a new log level: HEADERS_AND_ARGS
Bump test dependencies.
Patch Converter typo
Merge pull request #581 from f2prateek/patch-1

Patch Converter typo
Unexpected mime type should be a ConversionException.
Merge pull request #601 from square/ray/wire-conv

Unexpected mime type should be a ConversionException.
@Path/Query exception message update
Merge pull request #597 from austynmahoney/am/bug/595-path-query-exception

@Path/Query exception message update
Update GSON to 2.3
Merge pull request #605 from timehop/update-gson-dependency

Update GSON to 2.3
Use charset to properly adhere to Javadoc contract.
Merge pull request #610 from square/jw/gson-charset

Use charset to properly adhere to Javadoc contract.
Support multivalues in @QueryMap and @FieldMap parameters.
bump version