Rename re2_filter and re2_matcher to regexp_*

Working for replacing to oniguruma from re2.
Add --enable-re2 option to use re2.
Currently configure to use oniguruma by default.
Make googletest not to include regex.h

Add -DGTEST_HAS_POSIX_RE=0 cxxflag for testing
oniguruma matcher/filter.
googletest includes POSIX regex.h that conflicts
oniguruma definitions.
Implement oniguruma matcher
Implement oniguruma filter
Fix key_matcher_factory_test for oniguruma
Add illegal test to regexp_filter_test
Support regexp which matches empty string
add one test
add oniguruma setting in travis.yaml
substitution test
sudo is needed to install oniguruma
Merge pull request #465 from jubatus/feature/oniguruma

Add oniguruma based matcher and filter replacement for re2: fixes #361