expand tabs in documents

(cherry picked from commit 9cd4fa124a76baacdf929a9b1bdb943781317836)

Conflicts:

	HISTORY
	doc/API
	doc/API.ja
fix typo in doc/RE.ja (Close #28)

(cherry picked from commit 0747194fb5b88a8bb276600d1c02a1b00f2f33ec)

Conflicts:
	doc/RE.ja
import Oniguruma 5.9.5
Merge tag 'Oniguruma-5.9.5' into onig-5.9.x-mod

The original version of Oniguruma 5.9.5

Conflicts:
	regcomp.c
	st.h
remove unused variable

Do not use C99 style comment.
change the type of OnigCodePoint

There is no need of using 64-bit type for OnigCodePoint, 32-bit type is
enough.
[dist] update .editorconfig

Disable the trim_trailing_whitespace setting to reduce unnecessary
differences, because the original source codes of oniguruma contains
some trailing white spaces.
Merge branch 'onig-5.9.x-mod' into onig-5.9.x-mod_for_bregonig-v2