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/objc/m/class method.snippet

@@ -0,0 +1,4 @@
++ (${1:id}) ${2:method}
+{${3}
+	return nil;
+}

sources_non_forked/snipmate-snippets/objc/m/method.snippet

@@ -0,0 +1,4 @@
+- (${1:id}) ${2:method}
+{${3}
+	${4:return nil;}
+}