Updating uv_queue_work for Node 0.10 compatibility

uv_queue_work now needs its last argument casted. 

Also a mention in the readme that node-gyp is needed to build this.

a similar fix for sqlite3 node 0.10 compatibility can be seen here: https://github.com/jbuck/node-sqlite3/commit/837d8b06ced459301d86bdd9b099726b7916d6e0