Updated all plugins that are non-forked. Added some new plugins.

Added update_plugins.py which can fetch new plugins from GitHub.

New plugins added: zencoding, vim-indent-object, taglist, nginx.vim

sources_non_forked/snipmate-snippets/ruby-shoulda/selir.snippet

@@ -0,0 +1 @@
+should_ensure_length_in_range :${1:field}, ${2:start}..${3:end}