unquote now applies to the closest quote
Allow unquote in def*/2

This makes meta-programming in Elixir much easier and more friendly.
For example, here is how to convert a keywords argument into a bunch
of functions:

    Enum.each [foo: 1, bar: 2, baz: 3], fn { k, v } ->
      def unquote(k)(), do: unquote(v)
    end
Update CHANGELOG
Fix formatting and examples in CHANGELOG
Support unquoting on Macro.escape
Allow dynamic dispatch names on defdelegate
Clean up Unicode using the new unquote fragments
Use unquote instead of @ in HashDict
Ensure Macro.escape also respects nested quotes