Add profile support

Simple use cases:

• catalysts provide a trivial example to build in, used to disable scoverage
• Cross build for Scala.js 0.6.x and 1.x Cross build for Scala.js 0.6.x and 1.x cats#2195

also see cats discussion in later part of typelevel/cats#2130

@alexandru I know we discussed this before, but I really can't recall the details 😊

Do you still have any thoughts/ideas on this, please, before I get stuck in?

Another example from shapeless

I know we discussed this before, but I really can't recall the details

Now I do....https://github.com/technomancy/leiningen/blob/stable/doc/PROFILES.md