v0.13

    - Fix a long-standing bug of being unable to define constants from
      sub-packages at "call" time.

      If you were in the callback for YourExporter::CONSTANT and
      required a module that also used YourExporter module to get some
      YourExporter::UNRELATED_CONSTANT we wouldn't create that symbol
      for that module and we'd most likely die at compile-time.

      The reason for this is that we had a really naïve notion of when
      we should be interning constants purely based on whether we were
      in a nested "call" subroutine. Now we keep track of what
      constants packages want and intern those symbols they request.

    - We now use FATAL "recursion" warnings in Constant::Export::Lazy,
      if we've gone above perl's built-in recursion limit of 100 we'd
      rather die early than slowly exhaust all the memory on the
      system and have the OOM killer kill us when this happens.

    - Get rid of the Constant::Export::Lazy::Ctx::new()
      method. Instead we just bless directly into the package, this is
      just a nano-optimization.

    - Add a new test to see if we're actually defining constants, this
      test piggy-backs on the warnings emitted when our constant
      subroutines are overridden.

    - Clarify & reword some POD & inline comments.