Add an annotation for "units"

[jmeaster30]

Add an annotation for units that goes on function parameters or variable declarations.

This would let the compiler emit a warning/error for mismatched units

Not sure if this needs to be a language feature or if it can be implemented in the standard library.

[jmeaster30]

It would be cool to do:

function add3centimeters(@unit(cm) num: f64) -> (@unit(cm) result: f64 = num + 3cm);

let a = 10m;
let total = a.add3centimeters(); # this will throw an error saying "Parameter must have units as 'cm' but got a unit of 'm'."

Which makes me think of a couple things that are needed:

• language feature to have all units built in or let the user define them (now the parsing step seems to modify the lexing step?)
• ability to have inline annotations (what if all non block annotations look like function calls with named parameters?? Or like c#/rust object initialization. Then it would be a bit easier for an annotation parser i think and there could be like some type checking kinda)