Varnish Lexer: Add analyse_text()
Varnish Lexer: Add analyse_text()

It looks for documents starting with 'vcl 4.0;', optionally with comments
preceding it. As all valid VCL as of Varnish 4.0 starts with this (even
Varnish 4.1), this is pretty much guaranteed to work.

aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments