Remove support for node < 4.x

[brianc]

Dropping older versions of node out of the travis test matrix, allowing us to move away from some of the extremely old buffer APIs and move a bit more quickly on new features. For older versions the suggestion will be to use the 6.x trunk. We'll need to cut a maintenance branch we can back-port any critical security fixes to.

[vitaly-t]

You may want to use the same technique as I did within pg-promise.

See the library's entry file: lib\index.js.

The main reason behind such separation is to be able to use the ES6 syntax right from the library's main file (main.js in my example).

[brianc]

This is complete.