Use maruku on GitHub instread of 0.6.0.

0.6.0 (and 0.6.1) in Rubygems has problem with parsing Japanese markdown.
Translated backing services.
Fix phrasings.
Translated TOC until section 4.
Added information about translation into footer.
Remove untranslated sentences.
Standardlize phrasings of "twelve-factor app".

Use "Twelve-Factor App" or "Twelve-Factor".