Cross-build for ScalaJS and Scala Native.

[arturaz]

Resurrection of #9

Now it should work, I ran ++ test (tests on all platforms) on my machine.

I had to:

• resort to simple Random on JS/native platforms, as SecureRandom is only available on JVM.
• shuffle some code around to allow that.
• drop Scala 2.11 support, as js & native do not support it as well.

[arturaz]

Anything else I can do to get this merged?