Add mc, m snippets; fix once, head

vim/snippets/c.snippets

@@ -4,7 +4,6 @@ snippet uchar
 	unsigned char
 snippet ulong
 	unsigned long
-
 snippet head
 	/* `expand('%:t')`
 	 *
@@ -12,7 +11,8 @@ snippet head
 	 *
 	 * `g:snips_author`
 	 */
-
+	
+	 ${2}
 snippet main
 	int
 	main(int argc,
@@ -35,3 +35,22 @@ snippet pragma Ignore warning
 	${0}
 	
 	#pragma clang diagnostic pop
+snippet once
+	#ifndef ${1:`expand('%:t')`}
+	#define $1
+	
+	${2}
+	
+	#endif /* $1 */
+snippet mc
+	/*
+	 * ${1:Function} --
+	 *
+	 * ${2:Description}
+	 */
+snippet m
+	${2:void}
+	${1:Function}(${3:/* args */})
+	{
+		${3}
+	}