Add support for the Varnish VCL edge scripting language

Kind of ugly but the Perl lexer actually does a surprisingly good job and it's what we use internally at Fastly
See
https://gist.github.com/simonwistow/17c5ec92816149d8bed6
https://gist.github.com/simonwistow/2fa534508a3f6ae72508

as included in

http://www.fastly.com/blog/how-to-cache-with-tracking-cookies/#.U5IeJZSwI1o

I I get some more time I'll write a custom lexer for Pygments.

There's plenty of other references to VCL on Github

https://github.com/varnish/Varnish-Cache
https://github.com/thenextweb/wp-vcl
https://github.com/comotion/security.vcl
https://github.com/lampeh/varnish-vcl