Document how spellcasting proficiencies work

[MNG-cataclysm]

Summary

Mods "Document how spellcasting proficiencies work."

Purpose of change

Spellcasting proficiencies are a feature I added to Magiclysm in February, and it's since undergone a few changes. However, I failed to document how it worked, so this fixes that.

Describe the solution

Add documentation on how spellcasting proficiencies work, including explanations of the spell classes, how the JMATH works, how JMATH is used in spells, and some general advice for anyone using the system for their own content. I placed this in magic_balance.md, since spells were also documented there, and I added a table of contents due to the file's increased size, so it could be easier to navigate.

Describe alternatives you've considered

Not doing this and letting everyone figure it out on their own.

Testing

No testing needed; this is exclusively documentation. Everything looks nice when I peeked at it in GitHub's web page.

Additional context

@Standing-Storm @Maleclypse If you want to look over this and tell me what you think, I'd appreciate it.

[Maleclypse]

This is definitely helpful. Once Standing Storm has a chance to look at it and give any feedback I think this will be good to go.

[Standing-Storm]

One thing I'm curious about (since I just PRed a spell that violates these rules) is where debuff spells go. I figured enhancement, since it's changing the target's capabilities, but the docs say:

Any spells which exclusively debuff or hinder something should also not be included

...but that doesn't leave short-casting, short-term debuffs with a good category to fit into, unless Evocation is supposed to be the "odds and ends go here" category.

Edit: There's probably not a lot of debuff spells because when Magiclysm was first made monsters couldn't take enchantments, but now they can.

[MNG-cataclysm]

One thing I'm curious about (since I just PRed a spell that violates these rules) is where debuff spells go. I figured enhancement, since it's changing the target's capabilities, but the docs say:

Any spells which exclusively debuff or hinder something should also not be included

...but that doesn't leave short-casting, short-term debuffs with a good category to fit into, unless Evocation is supposed to be the "odds and ends go here" category.

That sort of spell would go in Evocation. If there gets a point where there's a lot of similar debuff spells, I'll probably make a proficiency for it. Call it Hexing or something like that.