Added Informix-4GL lexer

[arielvega]

Hi,

I have done this lexer some time ago because my need of support for this language, I think that this can be useful for the comunity.

###################### LEXER INFO ###################### title "4GL" desc "Informix-4GL is a 4GL programming language developed by Informix during the mid-1980s." tag '4gl' filenames '*.4gl' mimetypes 'text/plain'

I have added a lexer file in lib/rouge/lexers/4gl.rb, a demo file in lib/rouge/demos/4gl, spec/lexers/4gl.rb and in spec/visual/samples/4gl

Regards,

Ariel