Introduced `ExecutableContainer` and `LibraryContainer` added by the binaries plugin.
Renamed BinariesContainer to BinaryContainer
Renamed 'compilers' extension added by the binaries plugin to 'toolChains'.
Moved stale class cleaner out of public api
Added javadocs and include `org.gradle.language` in the API docs.
Added the extensions added by the `cpp` plugin to the DSL reference.