Translate chapter title
Translate 1-git-branching
Apply v1's translation
Translate additional contents
Update status
Correct mistranslation

see: https://github.com/progit/progit2-ja/pull/5#discussion-diff-20081283
Fix mistranslation

see: https://github.com/progit/progit2-ja/pull/5#discussion-diff-20082318
Tweak translation

see: https://github.com/progit/progit2-ja/pull/5#discussion_r20080992
Merge pull request #5 from m-takagi/translate-03-git-branching

Translate Chapter3 "Git Branching"