Split the macros for the RMxAA and RMxAC into separate files

[will-henney]

Request from Silvia and Chris:

1. Instead of having one class file rmaa.cls with proceedings and journal option, there will instead be separate class files. For instance rmxaa.cls for the main journal and rmxac.cls for the conference proceedings.

2. Each will have its own web page and instructions.

[will-henney]

Tests of how this can be implemented are now complete. The plan is to make use of Docstrip's conditional inclusion via nested guards. We define two guards: j-class for the journal class file (rmxaa.cls) and p-class for the proceedings class file (rmxac.cls) . The majority of the code is common to both, so we wrap the entire class code in j-class|p-class, and then use the specific guards for the few cases where the code differs between the two. So, it looks like this (image since GitHub doesn't fontify the %< tags properly):

Example is in source/test-split-macros/test-split-macros.dtx, which is based on a skeleton file in Scott Pakin's DTX tutorial.

[will-henney]

Only thing left on this issue is now sorting out the packaging and documentation.