Add regexp_splitter for builtin word splitter

Make re2_splitter builtin function and create new splitter
which supported oniguruma library.
Write test for empty match and fix it
Append check code
Insert static_cast to sepcify method to call
Merge pull request #510 from unnonouno/fix-onig-split

Write test for empty match and fix it
Eliminate moved test
Merge pull request #494 from jubatus/feature/onig_splitter

Add regexp splitter replacement for re2_splitter: fixes #471
version aware mix
send_model() implemented
put_diff should return boolean
online model_copy implemented and just work
delete debug_output in previous commit
-j option is not need, you should set zk and name
linear_mixer should be `obsolate` at the first state
mocks in tests should inherit get_model() function
Merge pull request #513 from unnonouno/fix-save-for-clang

Insert static_cast to sepcify method to call
Merge branch 'develop' of github.com:jubatus/jubatus into feature/online_model_copy