Integer precision of function return types

[Per Nordlöw]

Should a function like

```d
uint parseHex(in char ch) pure nothrow @safe @nogc {
	switch (ch) {
	case '0': .. case '9':
		return ch - '0';
	case 'a': .. case 'f':
		return 10 + ch - 'a';
	case 'A': .. case 'F':
		return 10 + ch - 'A';
	default:
		assert(0, "Non-hexadecimal character");
	}
}
```

instead return an ubyte?