Set development version to 2.3.0-SNAPSHOT.
Implemented of WINRM_NATIVE (winrs) connection type. Fixes #12.

The old, Java-based WINRM connection type has been renamed to WINRM_INTERNAL.
Code, logging and error message cleanup.
Fixing licenses.

- Added to files where missing.
- Updated year span to 2008-2013.
- Changed from Javadoc comment into regular comments.