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.