Add Support for Functions Within Functions

[RubyTheRoobster]

Several months ago, I scrapped the idea of functions within functions, because a function like:

x1*f(x2), where

f(x2) = g(x2) and g(x2) = x2.

would be too complicated to validate and execute at runtime. The solution? Evaluate functions within functions as expressions right before validation. This would write:

f(x2) = g(x2) = x2, and

x1f(x2) = x1x2,

all before the function is even validated! I'm surprised I didn't think of this before.

[RubyTheRoobster]

Or not. So it turns out, such a simple evaluation won't work, as I'm trying to make a generic library as possible. I can probably still make this work, but it's going to increase compile time by an unimaginable amount.

[RubyTheRoobster]

This has been put on hold, as there are more pressing issues on the roadmap.