Inconsistent casing in Lines and LineCodes for rmatrix, xmatrix and cmatrix

Currently the ODD interface exposes the following functions:

```
Lines.RMatrix
LineCodes.Rmatrix

Lines.XMatrix
LineCodes.Xmatrix

Lines.CMatrix
LineCodes.Cmatrix
```

It would be nice if these are consistent. @tshort, @PMeira any preferences?

The C API uses `Lines_Get_Rmatrix`, `LineCodes_Get_Rmatrix`, etc. So my vote is to use the same casing, i.e. change the functions in the `Lines` module. I believe the COM interface in the official distribution also uses this casing here.

The main reason I'm opening an issue for this is that this is technically an API breaking change, so it would require a major version update. But given that `v0.5.0` hasn't been updated on the METADATA.jl yet, it might be safe to assume no one is using the tagged `v0.5.0` version yet and maybe we can get away with the change in `v0.5.1`. Thoughts?

Alternatively, we can go with deprecation warnings and remove the other functions in the next major release.

Start by locating the Julia definitions and exports for the Lines and LineCodes modules, then inspect any tests covering RMatrix, XMatrix, and CMatrix. Confirm which casing is currently public and check how compatibility or deprecation is handled elsewhere; done means the casing policy is implemented consistently with appropriate coverage and the release decision is resolved.

Written by the indexing model from the issue text.