Parse new macro declarative expression

[GrayJack]

As reference:

1. Tracking issue: declarative macros 2.0 rust-lang/rust#39412
2. Macros by example 2.0 (macro!) rust-lang/rfcs#1584
3. https://github.com/rust-lang/rfcs/blob/master/text/1584-macros.md

[GrayJack]

One think that it will fix is namespaced macro calls as well, like path::to::macro::call!()

[Stargateur]

This make all color fail every time I write some_module::macro_name!(). I like to avoid import too many into my namespace.