Parse quote characters

[Yirmandias]

• Modification of the parse function to support quote, quasiquote and unquote characters.
• Modification of enum Token:

enum Token {
    Sym { start: usize, end: usize, start_pos: Pos },
    LParen(Pos),
    RParen(Pos),
    //new fields
    Quote(Pos),
    QuasiQuote(Pos),
    Unquote(Pos),
}

• Modification of the function tokenize to support new kind of Token.
• Modification of read to transform new tokens into corresponding symbols and construct and SList containing the quote expression.

[arbimo]

Clippy errors are likely due to the release of Rust 1.54 that has new clippy rules automatically picked up by CI. I have addressed them in master and you can simply rebase.

[arbimo]

need to fix this and the the tests for contextual display.
My intuition is that the span should finish at the end of e

[Yirmandias]

The function to get the end of e returns a Loc object.

e.loc().end() -> Loc.

From this Loc we cannot get the end Pos

[arbimo]

Essentially, you need e.span.end.
span is private is this case but you can add an accessor for the start and end Pos of a Loc

[arbimo]

Looks good to me. There are just 3 minors changes I commented on.

At this point it might be good to split the Atom between a String, a symbol and a number. This could be done in another PR however.