Avoid garbled in "text" section.
Translate "Other Input Plugins" for Japanese.
Fix typo.
Add categories and articles to ToC for Japanese version.
Translate some parts of "Buffer Plugin Overview" for Japanese.
Merge pull request #70 from fluent/hotfix/avoid_mojibake_in_in_forward

Avoid garbled in "text" section.
Translate "memory Buffer Plugin" for Japanese.
Translate "file Buffer Plugin" for Japanese.
A minor fix.