Add option to disable asynchronous diffs.

Closes #318.

README.mkd

@@ -187,6 +187,7 @@ You can customise:
 * Whether or not line highlighting is on initially (defaults to off)
 * Whether or not vim-gitgutter runs in "realtime" (defaults to yes)
 * Whether or not vim-gitgutter runs eagerly (defaults to yes)
+* Whether or not vim-gitgutter runs asynchronously in NeoVim (defaults to yes)
 
 Please note that vim-gitgutter won't override any colours or highlights you've set in your colorscheme.
 
@@ -299,6 +300,15 @@ Add `let g:gitgutter_signs = 0` to your `~/.vimrc`.
 Add `let g:gitgutter_highlight_lines = 1` to your `~/.vimrc`.
 
 
+#### To turn off asynchronous updates
+
+By default diffs are run asynchronously in NeoVim.  To run diffs synchronously instead:
+
+```viml
+let g:gitgutter_async = 0
+```
+
+
 ### FAQ
 
 > Why can't I unstage staged changes?

autoload/gitgutter/diff.vim

@@ -127,7 +127,7 @@ function! gitgutter#diff#run_diff(realtime, preserve_full_diff)
     call setbufvar(bufnr, 'gitgutter_tracked', 1)
   endif
 
-  if has('nvim') && !a:preserve_full_diff
+  if g:gitgutter_async && has('nvim') && !a:preserve_full_diff
     let cmd = gitgutter#utility#command_in_directory_of_file(cmd)
     " Note that when `cmd` doesn't produce any output, i.e. the diff is empty,
     " the `stdout` event is not fired on the job handler.  Therefore we keep

doc/gitgutter.txt

@@ -126,6 +126,7 @@ You can customise:
 - Whether or not line highlighting is on initially (defaults to off)
 - Whether or not vim-gitgutter runs in realtime (defaults to yes)
 - Whether or not vim-gitgutter runs eagerly (defaults to yes)
+- Whether or not vim-gitgutter runs asynchronously in NeoVim (defaults to yes)
 
 Please note that vim-gitgutter won't override any colours or highlights you've
 set in your colorscheme.
@@ -266,6 +267,15 @@ Add to your |vimrc|
   let g:gitgutter_eager = 0
 <
 
+TO TURN OFF ASYNCHRONOUS UPDATES
+
+By default diffs are run asynchronously in NeoVim.  To run diffs synchronously
+instead:
+
+Add to your |vimrc|
+>
+let g:gitgutter_async = 0
+<
 
 ===============================================================================
 6. FAQ                                                           *GitGutterFAQ*

plugin/gitgutter.vim

@@ -49,6 +49,7 @@ call s:set('g:gitgutter_diff_args',                  '')
 call s:set('g:gitgutter_diff_base',                  '')
 call s:set('g:gitgutter_map_keys',                    1)
 call s:set('g:gitgutter_avoid_cmd_prompt_on_windows', 1)
+call s:set('g:gitgutter_async',                       1)
 
 call gitgutter#highlight#define_sign_column_highlight()
 call gitgutter#highlight#define_highlights()