Cross build for scala 2.13

[dipucian]

scala 2.13.1 is released, new projects would like to start with latest scala

[simerplaha]

This will be nice to get done. I think the only work required here might be to have 2.13 implementations of custom collection like Slice[T] and a few others used internally in core.

scala-collection-compat looks great but the documentation here says:

You can use the scala-collection-compat library, which makes some of 2.13’s APIs available to 2.11 and 2.12. This solution does not always work, for example if your library implements custom collection types.

Will get this done soon. I'm currently working on updating the documentation on the website which is long overdue.

[simerplaha]

This is done. I will release it soon.

[simerplaha]

Released in v0.10.6