Into<Channel> should be a specific trait. e.g. AsChannel

[museun]

This will allow for better coherence. The blanket Into from std lib for coherence breaks the current attempt.

Currently something like the following has problems:

struct S;
impl Display for S {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
        write!(f, "foobar")
    }
}

fn foo(d: impl Into<Channel>) { 
    let ch = d.into();
}

foo("foobar"); // works
foo(S{}); // does not work
foo(S{}.to_string()); // works

And a bit of bikeshed. ToChannel vs AsChannel (e.g. consuming or borrowing). With the way the Writer works, it doesn't need ownership because its just going to format a string in the end, so everything can be borrowed which would be concatenated with some static data.