Switch build system

[richardwillars]

Hi,

Please could you switch the build system to GYP from WAF? As detailed here the script doesn't build - nodejs/node-v0.x-archive#3633

As noted on the node.js blog, WAF has been deprecated in favour of GYP - http://blog.nodejs.org/2012/06/25/node-v0-8-0/

Great work btw - brilliantly useful library!

[marchaos]

I've added support for GYP (in a pull request).