implement compileIntoCurrentProcedure for if-else-chain expressions

[Honktown]

I want to use variables in conditionals for noise expressions. More complex functions can be implemented without doing work-arounds on map-gen. I was looking into atan2: have all the math correct for an accurate approximation, but no conditionals are available.

"condition-expression" isn't a valid type of expression, and using if-else-chain returns true for values > 0, false for values < 0 (and probably 0), but only takes literal-number's. There's no means of providing ordinary conditions (<, >, etc) documented anywhere, and I tried a bunch of things and looked all over.

I have example code for it, if examples would like to be taken for no-error/error arguments.

[Honktown]

Nevermind, I figured out something for conditionals.

[Bilka]

I added this in 0.18.37.