- Allowed builtins to self-describe
- Broke builtins into their own module
- Created a macro to work with BuiltIns easier
- Uses macro 2.0 syntax, so it requires passing in ALL externally referenced identifiers
- Luckily, this is already a requirement of good, readable macro definitions!
- As a temporary hack, turn overloadable operators into function calls
- This is kind of pointless at the moment, since there can only be one definition of a function per name (no ADL/function overloading/traits/type namespaces yet!)
- This is also pretty slow, but benchmarking shows it's not as slow as I thought (~400x slower in release mode than a native Rust implementation when running `fib.cl`/`fib.rs`. Totally unacceptable for most work, but this is a tree walk interpreter.)
- TODO: Remove this when desugaring from operators to function calls is implemented
