Update version to 2.3.0

Manual version number update.

Merge pull request #86 from timburks/travis-linux

Add ubuntu.sh setup script and configure travis to test both osx and linux.

Merge pull request #83 from timburks/three

Merge "three" branch to master

Merge pull request #85 from christopherdumas/patch-1

A nicer, more centralized README

includes automatic markup operators (2.1) and a small change to

allow colons (:) to appear in markup attributes.