[TM-7] Implement and document some Morley language extensions (jcb/tm7-language)

Description

[General] Modularize Parser into:

• Morley.Parser
• Morley.Default
• Morley.Parser.Annotations

[TM-7] Implement and document some Morley language extensions:

• Tuple pairs: (pair a b) ~ (a, b)
• Nested tuples: (a,(b,c) ~ (a,b,c)
• Bar unions: (or a b) ~ (a | b)
• Nested unions: (a | (b | c)) ~ (a | b | c)
• Slash lambda: (lambda a b) ~ (\ a -> b)
• Paren unit: unit ~ (), Unit ~ ()
• Container type syntax: list a ~ [a], set a ~ {a}
• Lower case ops: e.g. DROP ~ drop

Related issue(s)

https://issues.serokell.io/issue/TM-7

• Implements basic extensions

✅ Checklist for your Merge Request

Related changes (conditional)

• Tests

  • If I added new functionality, I added tests covering it.
  • If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.

• Documentation

  • I checked whether I should update the docs and did so if necessary:
    • README
    • Haddock

Stylistic guide (mandatory)

• My commits comply with the following policy.
• My code complies with the style guide.