Add support for Deprecated annotation

[jwoertink]

You may have a setting you want to deprecate:

@[Deprecate("This is no longer used")]
setting old_setting : String

[jwoertink]

Turns out that this is not currently possible to do without a major refactor. Crystal has no way to detect annotations on a macro calls. So this annotation would have to be attached to a method, or instance variable, or module.

A "hack" could be something like this

macro setting(decl, ....)
  module MACRO_SETTING__%temp
  end

  {% ..... << {annotations:  MACRO_SETTING__%temp.resolve.annotations }%}
end

but this would also lead to some other issues... so for now I'll just have to figure out how to refactor this whole deal.