Pop context changes

[dkmk100]

This adds two main changes:

SpellContext#pop now takes a boolean for whether a filter passed

• if it did, it behaves as before
• if not, the default behavior is to
• the boolean is passed to the context manipulator
• Anything that doesn't do any filtering, like linger and burst, just passes true obviously

Spell Validator added

• context manipulators can accept or veto a context creator
• holds a set of context creators which glyphs can add themselves to
• ensures nested glyphs are legal to prevent things like a linger inside a burst

Finally: showcase glyphs which aren't meant to be in the final mod but show why addons need the two above features:

• else glyph: can follow after filters, and allows something else to run if they fail
• example filter: a filter to help showcase