Atom GLM language support

For years now I’ve been interested in the GridLAB-D power system simulation project. A core piece of the interface are the GLM files which contain the models to simulate, and possibly even the data used in the simulations. Starting my journey into GridLAB-D, I quickly became aware of the lack of GLM syntax highlighting. The syntax is broadly related to the syntax of C++, but that is hardly supporting the editing process. Having just acquired some experience in creating highlighting support in the Atom text editor in the context of the Asciidoctor projects, I decided to use my skills to create proper highlighting.