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
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