Add markdown plugin

packages.vim

@@ -63,6 +63,18 @@ Plug 'ledger/vim-ledger'
 Plug 'elzr/vim-json'
 Plug 'kchmck/vim-coffee-script'
 
+function! BuildComposer(info)
+  if a:info.status != 'unchanged' || a:info.force
+    if has('nvim')
+      !cargo build --release
+    else
+      !cargo build --release --no-default-features --features json-rpc
+    endif
+  endif
+endfunction
+
+Plug 'euclio/vim-markdown-composer', { 'do': function('BuildComposer') }
+
 call plug#end()
 
 " vim:ft=vim foldmethod=marker