layout qualifiers are not properly parsed

[ozthekoder]

Hey there! I have been looking for a useful glsl parser - ast builder. I have found this one to be quite good. Thank you for your hard work. One problem that I have encountered is that layout qualifiers are not recognized. I know this project hasn't been touched for years however it is still relevant and I would appreciate it if you could fix this issue. My problem is that I have no prior knowledge of bison or flex, even if you cannot work on this right now, at least give me some direction as to how to fix it, and I will gladly make a PR for it. Thanks.