Remove the need for specifying R leftover environment (continuation)

[gaelrenoux]

OK, I've taken @kitlangton's proposal from #23 and applied it to all *R methods. And behold: no more explicit environment declared when calling those methods! See discussion on that PR for details.

Also fixes the compile test that were not breaking compilation when they should.

[hmemcpy]

Hey, sorry to bump this, but I wanted to share something we use internally:

  def transaction[E, A](tx: ZIO[Connection, E, A]): ZIO[Transactor, E, A] =
    Database.transactionOrDie(tx)

  def transaction[R, E, A](tx: ZIO[Connection with R, E, A])(implicit ev: R <:< Has[_]): ZIO[Transactor with R, E, A] =
    Database.transactionOrDieR(tx)

A very thin wrapper, delegating to tranzactio. I was able to create two overloads called transaction. Normally this doesn't work, since [E, A] and [R, E, A] have the same erasure, but turns out that sticking an implicit causes them to be different as far as Scala is concerned!

So I can have my cake and eat it too - a single transaction function (from the user's perspective) that handles either Connection or Connection with R.

Not sure if that ship had sailed (now that you've published v2.0), but maybe you could use this trick and remove the R overloads completely! :)

[gaelrenoux-datadome]

@hmemcpy That's pretty interesting actually, it should work. The good thing is, I can put it into a 2.1.0, and just keep the *R methods as deprecated (there wouldn't be an issue here). I'll look into it (not sure when).