Update to use Kotlin 1.5 features

[DorianSnowball]

Kotlin 1.5 released lately and there is at least one feature that may be worth implementing:
Unsigned integer types

We could replace the logic where we check that variables are in a given range at least partially by using unsigned integers.

[Firionus]

Unfortunately we can't replace any of the existing logic as we'd need u9 and u15 for DmxAddress and ArtNetAddress respectively. Both do however need some changes (#41).
UByte might get handy when storing DMX values but let's see how the interaction with LibArtNet works out, it's a Java library.