add Changes that is revision history file
Separate git-gutter-fringe to another repository

  See also 'https://github.com/syohex/emacs-git-gutter-fringe'
remove git-gutter-fringe
Fix deleting all buffer overlay problem

The problem is following
 1 You enable git-gutter some buffers
 2 You call git-gutter:clear at the buffer
 3 All of git-gutter overlays are deleted

Why this problem occurs, because git-gutter:overlays
is global-variable. So I fix this variable to buffer local variable.
bumpup version and update Changes
Fix data structure

I don't use 'struct' for plugins
bumpup version and update Changes
add section of implmenting you own git-gutter
update test
update README.md
update diffinfo
fix for sample implementation information