Add Apache configuration language definition

Added Apache configuration language definition.

Supports:
* All official directives, both block and inline, up to Apache 2.4
* Block directive parameters separated by colon (*":"*)
* Comments (starting with *#*)
* Strings (both single and double quotes)
* Several variable styles (eg. *${HOME}*, *%{HTTP_REFERER}*, *$1*, *%2.1*, *%3+*)
* Variables in strings
* Regular expressions starting with "*^*" and/or ending with "*$*"
* Flags (eg. *[F]*)

Preview:
![prism_apacheconf3](https://cloud.githubusercontent.com/assets/6260786/4032552/582eeace-2c71-11e4-81ff-09c474a7bab0.PNG)
Well seen. I made the change for the regex. Thanks.

Regarding the directives groups, I'm not sure it's needed. It may shorten the line but we'd have to review all 600+ directives and it doesn't improve readability (in my opinion).