refactor: Make `selectors` field private

[volsa]

A little pet peeve I came across when using this library (it's awesome btw!) was rust-analyzer suggesting often times the initialisation of the Selector struct manually since the selectors field is public. This PR changes the visibility from

pub struct Selector {
    pub selectors: SmallVec<[parser::Selector<Simple>; 1]>,
}

to

pub struct Selector {
    selectors: SmallVec<[parser::Selector<Simple>; 1]>,
}

No breaking changes are introduced as the selectors field isn't used directly anywhere outside the module anyways.

[teymour-aldridge]

Thanks!

No breaking changes are introduced as the selectors field isn't used directly anywhere outside the module anyways.

This is technically a breaking change (because the Selectors struct is public, and could previously be constructed outside the module), which is fine (we'll just bump from v0.13 to v0.14 in the next release).

[volsa]

This is technically a breaking change (because the Selectors struct is public, and could previously be constructed outside the module), which is fine (we'll just bump from v0.13 to v0.14 in the next release).

Oh that's true, I just assumed everyone's using the parse function as documented. Anyhow, thanks for merging and maintaining this awesome library!

[cfvescovo]

Thank you for your contribution!