dsl: support press, more keys

[BrettMayson]

Alternative to #123

Adds more supported special keys
Add support for pressing a key {RETURN}

[pentamassiv]

I briefly had a look at it and I have some thoughts about it but I need a little more time to write a proper review. I should be able to do it this weekend

[pentamassiv]

It is a good start, but in my opinion the tokenize function needs a bigger refactor and we have to better define and document how the DSL works. I find it very hard to understand.
For example we have the following test:

fn success() {
        assert_eq!(
            tokenize("{{Hello World!}} {+CTRL}hi{-CTRL}"),
            Ok(vec![
                Token::Sequence("{Hello World!} ".into()),
                Token::KeyDown(Key::Control),
                Token::Sequence("hi".into()),
                Token::KeyUp(Key::Control),
            ])
        );
}

I would not have expected the Token::Sequence("{Hello World!} ".into()) to be correct here.

In the dsl.rs example we do
enigo.key_sequence_parse("{+UNICODE}{{Hello World!}} ❤️{-UNICODE}{+CTRL}a{-CTRL}");
but the function returns Err(UnknownTag("+UNICODE")). That probably is also not what we would want.

Because this PR and also #123 do not change the current behavior but at least fix #34, I am fine if either of them are merged.

[pentamassiv]

Feel free to merge it