add ISO referencing comment
support $; default splitter
support group name backref
improve error message and type
make GC free OnigRegion*
support CRuby global variables
add methods to disable setting global variables per each match
improve global variables tests and add tests for OnigRegexp.set_global_variables
use constants defined by oniguruma.h
add OnigRegexp.escape method
add ISO index to OnigRegexp.escape
Merge pull request #11 from take-cheeze/improvement

Improvement to CRuby like Regexp.