AutoValue Release 1.3-rc1

Functional changes

• Support for TYPE_USE @Nullable.
  This is #293 by @brychcy.
• Restructured the code in AutoValueProcessor for handling extensions, to get
  rid of warnings about abstract methods when those methods are going to be
  implemented by an extension, and to fix a bug where extensions would not work
  right if there was a toBuilder() method. Some of the code in this change is
  based on #299 by @rharter.
• Added support for "optional getters", where a getter in an AutoValue Builder
  can have type Optional<T> and it will return Optional.of(x) where x is
  the value that has been set in the Builder, or Optional.empty() if no value
  has been set.
• In AutoValue builders, added support for setting a property of type
  Optional<T> via a setter with an argument of type T.
• Added logic to AutoValue to detect the confusing case where you think you
  are using JavaBeans conventions (like getFoo()) but you aren't because at
  least one method isn't.
• Added a README.md describing EscapeVelocity.

Bugs fixed

• Allow an @AutoValue.Builder to extend a parent builder using the <B extends Builder<B>> idiom.
• AutoAnnotation now factors in package names when detecting
  overloads. Previously it treated all annotations with the same SimpleName as
  being overload attempts.
• Removed an inaccurate javadoc reference, which referred to an
  artifact from an earlier draft version of the Extensions API. This is
  #322 by @lucastsa.