Fix #13: Add UnPlug and g:plugs_disabled

It is now possible to either "UnPlug" plugins similarly
to how one would "Plug" them. Alternatively use the
`g:plugs_disabled` as a list of repo names to be disabled.

See comments in `.vimrc` and updated README for further
instructions and information.

.vimrc

@@ -20,14 +20,28 @@
         autocmd VimEnter * PlugInstall --sync | source $MYVIMRC
     endif
 
+    """ Plugins to be disabled {{{
+    """ https://github.com/timss/vimconf/issues/13
+        " Create empty list with names of disabled plugins if not defined
+        let g:plugs_disabled = get(g:, 'plug_disabled', [])
+
+        " Trim and extract repo name
+        " Same substitute/fnamemodify args as vim-plug itself
+        " https://github.com/junegunn/vim-plug/issues/469#issuecomment-226965736
+        function! s:plugs_disable(repo)
+            let repo = substitute(a:repo, '[\/]\+$', '', '')
+            let name = fnamemodify(repo, ':t:s?\.git$??')
+            call add(g:plugs_disabled, name)
+        endfunction
+
+        " Append to list of repo names to be disabled just like they're added
+        " UnPlug 'junegunn/vim-plug'
+        command! -nargs=1 -bar UnPlug call s:plugs_disable(<args>)
+    """ }}}
+
     " Default to same plugin directory as vundle etc
     call plug#begin('~/.vim/bundle')
 
-    " local plugins
-    if filereadable($HOME."/.vimrc.plugins")
-        source $HOME/.vimrc.plugins
-    endif
-
     " <Tab> everything!
     Plug 'ervandew/supertab'
 
@@ -86,6 +100,15 @@
         Plug 'majutsushi/tagbar'
     endif
 
+    " Local plugins
+    if filereadable($HOME."/.vimrc.plugins")
+        source $HOME/.vimrc.plugins
+    endif
+
+    " Remove disabled plugins from installation/initialization
+    " https://vi.stackexchange.com/q/13471/5070
+    call filter(g:plugs, 'index(g:plugs_disabled, v:key) == -1')
+
     " Initalize plugin system
     call plug#end()
 """ }}}

README.md

@@ -38,6 +38,24 @@ Some useful plugins could be:
 * [jedi-vim](https://github.com/davidhalter/jedi-vim) - Python autocompletion using the Jedi library.
 * [YouCompleteMe](https://github.com/Valloric/YouCompleteMe) - Autocompletion for several languages (C/C++, Python, ...)
 
+### Disabling plugins
+
+If you want to disable any of the plugins included in the main configuration
+either `UnPlug` them:
+
+```viml
+UnPlug 'ervandew/supertab'
+UnPlug 'scrooloose/syntastic'
+```
+
+Or define a list of repo names to be disabled:
+
+```viml
+let g:plugs_disabled = ['supertab', 'syntastic']
+```
+
+Both should be added to `~/.vimrc.plugins`.
+
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