Clean up RewriteRules

* Remove unnecessary "admin" Rewrites
* Simplify to a single `RewriteEngine on` declaration
* Wrap all RewriteRules in an `IfModule` conditional
* Add comment explaining "maintenance" rewrite
Ensure WP RewriteRule starts w/ a `/`

Hopefully fixes issue w/ wp-admin not rewriting properly
Add `/apc-nrp.php` exception to WP RewriteRules

Allows the Plugin Agent APC module to work properly
Update W3TC RewriteRules to match current configuration

Bump to 0.8.0