Document the VCL variables where we define them in generate.py.
Document the VCL variables where we define them in generate.py.

Initial doc pulled from vcl.rst

Generate doc/sphinx/reference/vcl_var.rst based on this.

varnish/Varnish-Cache,mrhmouse/Varnish-Cache,chrismoulton/Varnish-Cache,ajasty-cavium/Varnish-Cache,mrhmouse/Varnish-Cache,feld/Varnish-Cache,chrismoulton/Varnish-Cache,feld/Varnish-Cache,ajasty-cavium/Varnish-Cache,gauthier-delacroix/Varnish-Cache,chrismoulton/Varnish-Cache,varnish/Varnish-Cache,gauthier-delacroix/Varnish-Cache,gauthier-delacroix/Varnish-Cache,varnish/Varnish-Cache,mrhmouse/Varnish-Cache,ajasty-cavium/Varnish-Cache,franciscovg/Varnish-Cache,gquintard/Varnish-Cache,chrismoulton/Varnish-Cache,zhoualbeart/Varnish-Cache,gquintard/Varnish-Cache,zhoualbeart/Varnish-Cache,franciscovg/Varnish-Cache,mrhmouse/Varnish-Cache,zhoualbeart/Varnish-Cache,chrismoulton/Varnish-Cache,feld/Varnish-Cache,gauthier-delacroix/Varnish-Cache,ajasty-cavium/Varnish-Cache,feld/Varnish-Cache,zhoualbeart/Varnish-Cache,ajasty-cavium/Varnish-Cache,mrhmouse/Varnish-Cache,franciscovg/Varnish-Cache,zhoualbeart/Varnish-Cache,franciscovg/Varnish-Cache,gquintard/Varnish-Cache,alarky/varnish-cache-doc-ja,gauthier-delacroix/Varnish-Cache,alarky/varnish-cache-doc-ja,alarky/varnish-cache-doc-ja,alarky/varnish-cache-doc-ja,alarky/varnish-cache-doc-ja,franciscovg/Varnish-Cache,feld/Varnish-Cache,gquintard/Varnish-Cache,varnish/Varnish-Cache,varnish/Varnish-Cache