Implement `@` in compiler-in-Tamsin.  Only 36 fails now.
Implement `using` in compiler-in-Tamsin.  Only 6 failures now!
Don't emit decls for locals that are variables in patterns.
Implement $:hexbyte.  Tamsin-in-Tamsin has 8 failures, no cheating.
Add $:format_octal (sigh.)  Compiler-in-Tamsin has 6 failures.
Save/restore buffer in scanner.  5 failures now.
Haha, error in fixture.  Down to 3 failures now.
format_octal: no leading zeroes; specify one byte.
just a note
Add $:length and use in compiler.tamsin, which has 3 fails now.
TAMSIN COMPILER IN TAMSIN PASSES ALL TESTS