Improve asynchronous highlighting
add .gitignore
Fix process buffer issue

If users call dired-k in different directory between 1st time and 2nd
and 1st time buffer is still alive at 2nd time, result of `git status`
in 2nd time is same as 1st ones.
Merge pull request #3 from syohex/improve-for-asynchronous

Improve for asynchronous