Add option for <Esc> to close non-floating preview window

Closes #718.

autoload/gitgutter/hunk.vim

@@ -455,6 +455,9 @@ function! s:open_hunk_preview_window()
   setlocal filetype=diff buftype=acwrite bufhidden=delete
   " Reset some defaults in case someone else has changed them.
   setlocal noreadonly modifiable noswapfile
+  if g:gitgutter_close_preview_on_escape
+    nnoremap <buffer> <silent> <Esc> :pclose<CR>
+  endif
 endfunction
 
 

doc/gitgutter.txt

@@ -311,6 +311,7 @@ Signs:~
 Hunk previews:~
 
     |g:gitgutter_preview_win_floating|
+    |g:gitgutter_close_preview_on_escape|
 
 Terminal:~
 
@@ -468,6 +469,11 @@ Whether to use floating/popup windows for hunk previews.  Note that if you use
 popup windows on Vim you will not be able to stage partial hunks via the
 preview window.
 
+                                          *g:gitgutter_close_preview_on_escape*
+Default: 0
+
+Whether pressing <Esc> in a non-floating preview window closes it.
+
                                            *g:gitgutter_terminal_reports_focus*
 Default: 1
 

plugin/gitgutter.vim

@@ -73,6 +73,7 @@ call s:set('g:gitgutter_terminal_reports_focus',         1)
 call s:set('g:gitgutter_async',                          1)
 call s:set('g:gitgutter_log',                            0)
 call s:set('g:gitgutter_use_location_list',              0)
+call s:set('g:gitgutter_close_preview_on_escape',        0)
 
 call s:set('g:gitgutter_git_executable', 'git')
 if !executable(g:gitgutter_git_executable)