Handle %xx encoding in querystring

Convert valid %xx expressions in querystring to ascii, ignore invalid
expressions (i.e. eat the three characters %xx).

Signed-off-by: Lars Hjemli <larsh@hal-2004.(none)>

shared.c

@@ -113,3 +113,16 @@ void *cgit_free_commitinfo(struct commitinfo *info)
 	free(info);
 	return NULL;
 }
+
+int hextoint(char c)
+{
+	if (c >= 'a' && c <= 'f')
+		return 10 + c - 'a';
+	else if (c >= 'A' && c <= 'F')
+		return 10 + c - 'A';
+	else if (c >= '0' && c <= '9')
+		return c - '0';
+	else
+		return -1;
+}
+