Support Rust slice type

[czocher]

Adds support for the Rust slice type e.g.:

#[typeshare]
#[derive(Serialize)]
pub struct Video<'a> {
    pub tags: &'a [Tag],
}

@LouisGariepy please verify if it works in your case.

Closes #126

[LouisGariepy]

@czocher Tested your branch on my project and it seems to work as intended as far as I can tell. Thanks.

[Lucretiel]

This looks great! In the future, if it comes up, we can look at adding a warning for &[u8], which may not do what the user expects (both serde and typeshare will treat it as an array of integers rather than a byte blob), but we can leave that for if people have issues with it.