Allow for creating raw diffs with cgit_print_diff()

This adds a parameter to cgit_print_diff() to create raw diffs, using
the same format as `git diff <commit>`.

Signed-off-by: Lukas Fleischer <cgit@cryptocrack.de>

cmd.c

@@ -57,7 +57,7 @@ static void commit_fn(struct cgit_context *ctx)
 
 static void diff_fn(struct cgit_context *ctx)
 {
-	cgit_print_diff(ctx->qry.sha1, ctx->qry.sha2, ctx->qry.path, 1);
+	cgit_print_diff(ctx->qry.sha1, ctx->qry.sha2, ctx->qry.path, 1, 0);
 }
 
 static void info_fn(struct cgit_context *ctx)