Update and expand on plugin header information

PHP best practices are to include a 'DocBlock' at the beginning of
each file. Also, there are more fields supported and desired by WordPress
that were not previously included.
Bail if plugin file is accessed directly

Plugins shouldn't need to be able to execute PHP by direct URL
access. This change prevents that by checking if a WordPress
provided constant is defined.

This can be a security benifit depending on how the webserver
running the plugin is configured.
Miscellaneous formatting adjustments

- Removed extra blank lines
- Converted all text to use UNIX line endings
- Some spacing to conform with WordPress Coding Standards
- Converted indentation using spaces to tabs