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/html/form.snippet

@@ -0,0 +1,5 @@
+<form action="${1:action}" method="${2:post}" accept-charset="utf-8">
+  ${3}
+
+  <p><input type="submit" value="Continue &rarr;"/></p>
+</form>