Implement simple warning system based on type deduction

[ikskuh]

As all operators in LoLa are strictly type safe and don't do implicit conversions, the compiler can deduce a lot of variable types when compiling, even when no type annotation is given.

This allows the compiler to emit warnings/errors when type mismatches are possible:

var a = 10; // a is number
var b = a > 15; // b is boolen
return a + b; // this is a guaranteed type error as number != boolean

[ikskuh]

This is partially implemented already in the zig based compiler. Annotating variables doesn't work yet.