Support Scala 2.13

[jhnsmth]

scodec is now published for 2.13. so this project could move as well.
I could offer a help with it, if you are interested

[AdamChlupacek]

@jhnsmth hey there, help with this addition would be much appreciated if you have the time.

[jhnsmth]

@AdamChlupacek I'll give it a try on the weekend

[AdamChlupacek]

I have just released 0.4.0-M1 which is the first build with scala 2.13 support.