Merge pull request #492 from square/jw/deprecated

Remove deprecated functionality that has exceeded its grace period.
Move method init into try/catch so exceptions are properly propagated.
Merge pull request #494 from square/jw/init-in-try-catch

Move method init into try/catch so exceptions are properly propagated.
Update documentation for handling of @Field and @Part values.
Merge pull request #495 from square/jw/document-field

Update documentation for handling of @Field and @Part values.
Delegate to existing deserialization method.
Specify a useful message when creating a RetrofitError.
Merge pull request #496 from square/jw/exception-messages

Specify a useful message when creating a RetrofitError.
Change mock async behavior to use the supplied Callback instance directly.

This allows service APIs to use Callback subtypes and mock behavior together. Previously this would have thrown an exception due to the internal assumption that all asynchronous APIs were declared using Callback directly.