Docs: Update and improve `TOC.md`

* Make minor updates and improvements.
* Remove `.htaccess` mention as the Apache server configs are no longer
  part of the HTML5 Boilerplate core, plus, more information about them
  will be included in the `misc.md` file.
Docs: Update and improve `css.md`
Update to Apache Server Configs 2.6.0

Changelog: https://github.com/h5bp/server-configs-apache/blob/155b0b68c05b62e38781798bbd5fae2d6fcacf14/CHANGELOG.md#260-july-3-2014.