Emit an error event when something goes wrong, more closely mirroring the nodejs http module api.  This is done my assigning an onerror handler to xhr and propagating the event up.
Merge pull request #63 from klyngbaek/master

Emit an error event when something goes wrong...
1.5.0
Behave more like Node http regarding Buffers

Emit Node Buffers instead of ArrayBuffers
If encoding is null, return Buffer like in Node http