Evolutionary release with fixes and improvements implemented while working on
https://github.com/scalameta/tutorial.

The most prominent changes in comparison with 0.0.3 are:
  * Introduces a fallback dialect that materializes a dialect corresponding
    to the current compiler if the user doesn't specify anything explicitly.
  * Merges Mirror, Toolbox and Proxy into scala.meta.Context. Now we can simply
    tell people to "create a Context" without having to educate them about
    finer distinction between different contexts.
  * Tunes layout inference heuristic to support a bit more than just top-level
    definitions within simple packages. There is still much work to do,
    but it was enough for my Scala World demo.