Update code docs, fix invalid constant
Disable phpdoc generation in build for now
Bump version for 2.3.0-alpha development
Add dependency metadata/methods to xPDOTransport

Provides baseline support for dependency metadata to be specified and tested against version constraints
Add changelog entry
Add dependency metadata/API to xPDOTransport

Merge remote-tracking branch 'origin/pr/16' into develop

* origin/pr/16:
  Add changelog entry
  Add dependency metadata/methods to xPDOTransport
Merge remote-tracking branch 'xpdo/develop' into develop

* xpdo/develop:
  Add changelog entry
  Add dependency metadata/methods to xPDOTransport
  Bump version for 2.3.0-alpha development
  Disable phpdoc generation in build for now
  Update code docs, fix invalid constant