Add basic definition for black formatter.

README.md

@@ -137,8 +137,7 @@ Here is a list of formatprograms that are supported by default, and thus will be
 * `yapf` for __Python__ (supports formatting ranges).
   Vim-autoformat checks whether there exists a `.style.yapf` or a `setup.cfg` file up in the current directory's ancestry.
   Based on that it either uses that file or tries to match vim options as much as possible.
-  It is readily available through PIP.
+  Most users can install with the terminal command `sudo pip install yapf` or `pip install --user yapf`.
-  Most users can install with the terminal command `sudo pip install yapf` or `pip  install --user yapf`.
   YAPF has one optional configuration variable to control the formatter style.
   For example:
 
@@ -150,6 +149,10 @@ Here is a list of formatprograms that are supported by default, and thus will be
 
   Here is the link to the repository: https://github.com/google/yapf
 
+* `black` for __Python__.
+  Most users can install with the terminal command `sudo pip install black` or `pip install --user black`.
+  Here is the link to the repository: https://github.com/ambv/black
+
 * `js-beautify` for __Javascript__ and __JSON__.
   It can be installed by running `npm install -g js-beautify`.
   Note that `nodejs` is needed for this to work.

plugin/defaults.vim

@@ -52,8 +52,12 @@ function! g:YAPFFormatConfigFileExists()
     return len(findfile(".style.yapf", expand("%:p:h").";")) || len(findfile("setup.cfg", expand("%:p:h").";")) || filereadable(exists('$XDG_CONFIG_HOME') ? expand('$XDG_CONFIG_HOME/yapf/style') : expand('~/.config/yapf/style'))
 endfunction
 
+if !exists('g:formatdef_black')
+    let g:formatdef_black = '"black -q ".(&textwidth ? "-l".&textwidth : "")." -"'
+endif
+
 if !exists('g:formatters_python')
-    let g:formatters_python = ['autopep8','yapf']
+    let g:formatters_python = ['autopep8','yapf', 'black']
 endif