Fix #31 issue (Thanks hanabokuro)

sometime(eg ediff-mode) file become nil and cause error.
Bump up version and update Changes
fix typo
Improve sample code
Fix problem of first line revert
Merge branch 'support-add-p'
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Suppress byte compile warning
Implement git-gutter:stage-hunk

It is used like 'git add -p'
update document
fix invalid case for lacking newline
remove needless code
Merge pull request #32 from syohex/stage-hunk

Stage hunk
Bump up version and update Changes