Support { 'do': ':VimCommand' } notation

Close #450

README.md

@@ -201,6 +201,12 @@ Plug 'Shougo/vimproc.vim', { 'do': 'make' }
 Plug 'Valloric/YouCompleteMe', { 'do': './install.py' }
 ```
 
+If the value starts with `:`, it will be recognized as a Vim command.
+
+```vim
+Plug 'fatih/vim-go', { 'do': ':GoInstallBinaries' }
+```
+
 If you need more control, you can pass a reference to a Vim function that
 takes a single argument.
 

plug.vim

@@ -267,7 +267,7 @@ function! plug#end()
       syntax enable
     end
   else
-    call s:reload()
+    call s:reload_plugins()
   endif
 endfunction
 
@@ -275,9 +275,13 @@ function! s:loaded_names()
   return filter(copy(g:plugs_order), 'get(s:loaded, v:val, 0)')
 endfunction
 
-function! s:reload()
+function! s:load_plugin(spec)
+  call s:source(s:rtp(a:spec), 'plugin/**/*.vim', 'after/plugin/**/*.vim')
+endfunction
+
+function! s:reload_plugins()
   for name in s:loaded_names()
-    call s:source(s:rtp(g:plugs[name]), 'plugin/**/*.vim', 'after/plugin/**/*.vim')
+    call s:load_plugin(g:plugs[name])
   endfor
 endfunction
 
@@ -785,7 +789,12 @@ function! s:do(pull, force, todo)
       let error = ''
       let type = type(spec.do)
       if type == s:TYPE.string
-        let error = s:bang(spec.do)
+        if spec.do[0] == ':'
+          call s:load_plugin(spec)
+          execute spec.do[1:]
+        else
+          let error = s:bang(spec.do)
+        endif
       elseif type == s:TYPE.funcref
         try
           let status = installed ? 'installed' : (updated ? 'updated' : 'unchanged')

test/workflow.vader

@@ -933,11 +933,24 @@ Execute (Should not run when failed to update):
   Assert filereadable(g:plugs['vim-pseudocl'].dir.'/not-failed'),
     \ 'vim-pseudocl/not-failed should exist'
 
+Execute (Vim command with : prefix):
+  call plug#begin()
+  Plug 'junegunn/vim-pseudocl', { 'do': ':call setline(2, 12345)' }
+  call plug#end()
+
+  PlugInstall!
+  Log getline(1, '$')
+  AssertEqual '12345', getline(2)
+  q
+
 **********************************************************************
 ~ Overriding `dir`
 **********************************************************************
 
 Execute (Using custom dir):
+  call plug#begin()
+  Plug 'junegunn/vim-easy-align'
+  call plug#end()
   Assert isdirectory(g:plugs['vim-easy-align'].dir)
 
   call RmRf('/tmp/vim-plug-test/easy-align')