* protoc: added java support
Modified protoc to support also .proto -> .java generation. the .java file
name generated is not obvious as in C++/Python but follows a couple of rules
that were implemented.
As cxx/python and javaw Tools are quite different the implementation is not
as clean as for cxx/python but is hopefully fine (ie. protoc still uses
sources for input files while javac uses src_dir).
In javaw a small detail was added: a new attribute was added (gencode) that
instructs javac to look for source files also in the build directory. This
are realistically generated code (and .proto -> .java is an example) and
are therefore in the build. Default is false keeping all the previous
behaviour.
* protoc for java enhanchments (protoc version, regex, docs)
In configure stage get protoc version as java naming changes depending on the
version. Implement the version differences between version < 2 and > 2
Improve regex for option catching and implement a mix of them in playground
to verify it.
Add some documentation on how java filenames and paths are generated.
* protoc: build dir with generated code is automatically added, so no need to explicitly use gencode in javac
