implement support for EDoc annotations

[domnikl]

When documenting Erlang source files, EDoc annotations like in the example below should be shown also in the structure view, maybe even considered for code inspection.

%% @spec (list()) -> {bar, list()}
foo(Foobar) ->
    {bar, Foobar}.

Should show up in the structures view like this:

foo/1
    foo(Foobar::list())

[horkhe]

Tag @SPEC was deprecated long time ago. You should you use type specifications instead -spec. @ignatov since -spec is not yet fully supported by the plugin I would recommended to concentrate on it and leave edoc @SPEC for distant future when the plugin 100% implemented and you need something to get yourself busy :)

[yzh44yzh]

Yes, we should support -spec but not @SPEC