Merge pull request #12 from suzukaze/add-hset-hget-and-hdel

Redis#hset, hget and hdel method
replace RSTRING_PTR with mrb_str_to_cstr for null-terminated
Activate some test
change test type
Commented out some test for fail of travis gcc only
Add encrypted new webhook url
Add Redis#incrby
Merge pull request #13 from suzukaze/add-redis.incrby

Add Redis#incrby