Refactoring and cleaning up LogentriesAppender.cs.

Added ImmediateFlush property.
Cleaned up naming and casing.
Made variable and identifier names consistent.
Rewrote comments consistently.
Reorganized members.
Added regions.
Made most methods protected virtual.
Added a few missing exceptions in debug logging.
Rephrased error messages.
Merge pull request #8 from DanielStolt/master

Improved, refactored and cleaned up LogentriesAppender.cs.