A whole bunch of changes!

• Changed the default retrolambda to 2.0.0
• Added support for default methods, add defaultMethods true to the retrolambda block. Note: due to a current limitation in retrolamba, this will require all of your class files to be fed through retrolambda on each build. This may adversely affect build times.
• incremental false is no longer deprecated but has different semantics. Instead of being a hack around gradle-retrolambda breaking other plugins, it now only forces all of your class files to be run through retrolambda instead of only the changed ones.
• Added support for android unit tests, including lambdas in the tests themselves.
• No longer patch the android jar, modify the classpath instead. This should resolve issues with using gradle-retrolambda with more obscure android sdks, like google glass. This should also speed up a clean build since it doesn't have to do any zipping shenanigans.
• Ensure the gradle plugin is compiled with java 6 compatibility. This should allow you to run gradle with an older version of java if you don't want java 8 set as the default. This was always the intention, but was broken in the last build.
• More minor changes to how the java compile task is replaced, this should ensure better compatibility with other plugins. Note: these changes make the plugin application order more important. Make sure you you apply this plugin last.
• Removed 'retrolambda', now you can only apply the plugin with 'me.tatarka.retrolambda'.