Quasiquote syntax support

[NeilKleistGao]

Support more quasiquote syntax:

• Assign
• While
• NuNew
• Tuple
• Pattern matching

Also see: #182

[LPTK]

• A pattern like `f(a) is always wrong, as a quoted f can never be applied. We should issue a warning that the user probably intended to write `f`(a).

[NeilKleistGao]

• Improve quoted blocks:

  `let x = a `in
    `log`(x)
    x

  [@LPTK:] this should generate a warning as it's obviously not doing something the user expected. Similarly to `foo(`42) (should be `foo`(`42)).