fix a comment end of include guard
fix off-by-one error in String#rindex(fixnum)

null-terminated string should not be included in search targets.
Merge pull request #1792 from cubicdaiya/issues/fix_invalid_comment

fix a comment end of include guard
Merge pull request #1795 from cubicdaiya/issues/off_by_one_error

fix off-by-one error in String#rindex(fixnum)
Fix #1793
update compilation notes
fix typo
Merge pull request #1796 from mattn/fix_1793

Fix #1793
Merge pull request #1797 from take-cheeze/doc_update

Add notes about new features.