Upgrade to sbt 1.0.1 about iota HOT 1 CLOSED

@juanpedromoreno
https://github.com/frees-io/iota/tree/sg-port-to-sbt-1.0.x should be finished. Feel free to push/trash/cherry-pick the branch.

  def overrideSwitchCommand: Command =
    Command.arb(Cross.requireSession(Cross.switchParser), CommandStrings.switchHelp)(switchCommandImpl)		

This snippet was using a lot of now private methods in sbt 1.0.

So I ended up copy pasting most of the required snippets into:
https://github.com/frees-io/iota/compare/sg-port-to-sbt-1.0.x#diff-c3b7f539f0c1b9fcb3c518e0704ae7eb

Is there a better way? If not, there needs to be appropriate license headers and attribution for that file. As far I can tell, they are compatible(BSD/ASLv2)... There are a few methods that were written under ASLv2(before the copy/paste).
https://github.com/sbt/sbt/blob/v1.0.1/main/src/main/scala/sbt/Cross.scala

I removed fork in run := true, because bench/compile code generation didn't seem to be closing a file handle when forked.

iota has a dependency on cats 1.0.

Comparisons:
master...sg-port-to-sbt-1.0.x
port-to-sbt-1.0.x...sg-port-to-sbt-1.0.x

from iota.