API签名生成及验证

[Liu-Ameng]

参考:
http://developer.baidu.com/wiki/index.php?title=%E5%8F%82%E6%95%B0%E7%AD%BE%E5%90%8D%E7%AE%97%E6%B3%95&qq-pf-to=pcqq.c2c

Todo:
int str2md5(char str[], char md5[]);
int getToken[](char user_id[], char token[]);
int getSignature(char params[], char token[], char signature[]);
int checkSignature(char params[]);