Simplify sanitizeKey
Simplify sanitizeKey

Use a regular range and a switch to avoid a really long expression.

This also means that we now work with runes instead of bytes, which is
more intuitive. A non-ascii rune will now be turned into a single '$'
instead of multiple.

nebolsin/tyk,mvdan/tyk,nebolsin/tyk,mvdan/tyk,lonelycode/tyk,mvdan/tyk,lonelycode/tyk,nebolsin/tyk,nebolsin/tyk,mvdan/tyk,nebolsin/tyk,mvdan/tyk,nebolsin/tyk,mvdan/tyk,nebolsin/tyk,mvdan/tyk,nebolsin/tyk,lonelycode/tyk,mvdan/tyk