Merge Gslc into GslCore

[rmcl]

Hey @daz10000, I'm starting the work of releasing our integration tests and from what I see currently they would need to live in Gslc repo (https://github.com/Amyris/Gslc). I know each of our companies probably have an internal version of that repo that does our own peculiar and proprietary things. That said, as illustrated in this https://github.com/Amyris/GslCore/issues/1 coming up to speed with Gsl as an outside is a real tough lift because the relationship between the repos is not clearly defined and there are no good docs or examples on how to get setup. My perhaps naive proposal is to move the https://github.com/Amyris/Gslc/tree/master/src/Gslc dotnet project in to https://github.com/Amyris/GslCore/tree/master/src. Chris Dolan did some work internally to port that project to dotnetcore from the old mono setup. After that, we could push our integration tests into a test directory in the root of GslCore and they could be run on every change to GslCore.

Do you think this is a good idea? Happy to entertain alternatives if you have better ideas!