Signal macro

[jgcodes2020]

Implements a macro for signals. This is still really rough around the edges and doesn't support things like extension traits. I also need to figure out how to write tests for this thing.

[bilelmoussaoui]

Have you seen #1577 and the comments left there?

[jgcodes2020]

Have you seen #1577 and the comments left there?

Just took a look; I'm not sure if they're still working on it. Where my implementation differs (as far as I can tell) is being able to specify no class handler using:

#[glib::signals]
impl Base {
    #[signal(run_first)]
    fn one(&self);
}

Without the macro, rust-analyzer will correctly parse the function signature before erroring saying it doesn't have a body.