term: allow to disable the term extension

closes #1981

autoload/airline/extensions.vim

@@ -163,7 +163,8 @@ function! airline#extensions#load()
     call add(s:loaded_ext, 'netrw')
   endif
 
-  if has("terminal") || has('nvim')
+  if (has("terminal") || has('nvim')) &&
+        \ get(g:, 'airline#extensions#term#enabled', 1)
     call airline#extensions#term#init(s:ext)
     call add(s:loaded_ext, 'term')
   endif

doc/airline.txt

@@ -1098,6 +1098,13 @@ taboo.vim <https://github.com/gcmt/taboo.vim>
 * enable/disable taboo.vim integration >
   let g:airline#extensions#taboo#enabled = 1
 <
+-------------------------------------                        *airline-term*
+Vim-Airline comes with a small extension for the styling the builtin
+|terminal|. This requires Nvim or a Vim compiled with terminal support.
+
+* enable/disable terminal integration >
+  let g:airline#extensions#term#enabled = 1
+
 -------------------------------------                        *airline-tabws*
 vim-tabws <https://github.com/s1341/vim-tabws>