Switched Keen IO PHP SDK to use Guzzle Web Service Client

This PR presents wholesale changes to the current library.  So apologies that it overwrites or removes a lot of the existing code - though I think the proposed changes offers a lot of usability and benefit.

Changes allows support for:
Bulk Loading
Parallel Requests (...about as async as PHP gets)
Event Analysis
Data Extraction
API Resource definitions through Service Descriptions
Versioning

Future updates would include some missing admin operations (deleting collections, etc), saved queries support, and better parallel operations through a single client method... and more, as I think of them.