Updating readme and version

In preparation for moving to beta status, updating README based on some
common feedback, and bumping version.
Support level 4 of URI template RFC

Add support for the explode and strlen parameters in the spec.
This has made the combine function slightly unpleasant.
Level 4 URI template support

Cleanups based on full set of tests from the URI template repo.
Haven't included the negative tests, as I'm not totally sure how
to represent the failures in the library yet. Should be fairly
trivial to add in the future once the appropriate signalling is
worked out.
Remove trailing whitespace
Merge pull request #46 from ianbarber/master

URITemplate level 4 and README/Version update