Simplify asVersion()

By leveraging `get_object_vars($this)`, the static property arrays are no longer necessary.  The catch is that all exportable properties in child classes must not be `private`, or must be handled in a custom `_asVersion()` method.

When tests were added or modified, only minimal happy-paths were taken.  More robust testing is still needed for complete coverage.  The exception is `StatementTest` which had it's `testAsVersion()` updated to actually test functionality.  It's now the most robust test of `AsVersionTrait::asVersion()` in the whole suite.

I welcome your feedback and look forward to helping out and working with you on this and your other libraries.
Though the endpoint shouldn't have been in there, I don't know that we want to point this by default at the public endpoint either. If we want to we could set it to the travis-ci properties from https://github.com/RusticiSoftware/TinCanJava/blob/master/src/test/resources/travis-ci.properties since I plan to do that for all the libs, or better yet if you want to make it from a config file and provide a template + a travis ci file that'd be the best way to go.