Minor manual cleanup - inlined many format args. This makes the code a bit more readable, and helps spot a few inefficiencies and possible bugs. Note that `&foo` in a `format!` parameter results in a 6% extra performance cost, and does not get inlined by the compiler (yet).
- Change the main! proc_macro to a bin! macro_rules macro.
- Reexport uucore_procs from uucore
- Make utils to not import uucore_procs directly
- Remove the `syn` dependency and don't parse proc_macro input (hopefully for faster compile times)
