More flexible operands in KCL operators

[adamchalmers]

Currently KCL parser cannot handle using function calls as operands.

e.g. this works:

let x = f()
let y = x + 1

but this doesn't

let y = f() + 1

It should work, though!

[jtran]

This works, so maybe it was already fixed.

[jessfraz]

Huh we should make sure we have a test for it so it doesn't break