Create wrapper for GRM module - High level API

[kojix2]

One of the most wonderful features of GR is the GRM module. This is a module that takes advantage of the variable-length arguments of the C language, and by creating GRM bindings, you can immediately use practical visualization in any programming language. This is great.

However, GRM is a relatively new module. The old GR bindings, such as the Julia binding, do not use GRM. The high-level API is implemented in Julia. It is more advanced than GRM. However, re-implementing this in Crystal would be a challenge.

I don't have much time to devote to developing GR.cr, so I think it would be better to create a thin wrapper for GRM and make it a higher level API.