Gson 2.9.1

• Make Object and JsonElement deserialization iterative rather than recursive (#1912)
• Added parsing support for enum that has overridden toString() method (#1950)
• Removed support for building Gson with Gradle (#2081)
• Removed obsolete codegen hierarchy (#2099)
• Add support for reflection access filter (#1905)
• Improve TypeToken creation validation (#2072)
• Add explicit support for float in JsonWriter (#2130, #2132)
• Fail when parsing invalid local date (#2134)

Also many small improvements to javadoc.