Introduce prepend/append_multiline_delimiter

[nbacquey]

@append_multiline_delimiter / @prepend_multiline_delimiter

The matched nodes will have a multiline-only delimiter appended to them.
It will be printed only in multi-line nodes, and omited in single-line nodes. The delimiter must be specified using the predicate #delimiter!.

Example

; Add a semicolon at the end of lists only if they are multiline, to avoid [1; 2; 3;].
(list_expression
  (#delimiter! ";")
  (_) @append_multiline_delimiter
  .
  ";"? @do_nothing
  .
  "]"
  .
)

This allows proper formatting of the following:

let _ =
  [
    1;
    2;
    3;
  ]

let _ = [1; 2; 3]

Closes #199

[torhovland]

Suggested change

	It will be printed only in multi-line nodes, and omited in single-line nodes. The delimiter must be specified using the predicate `#delimiter!`.
	It will be printed only in multi-line nodes, and omitted in single-line nodes. The delimiter must be specified using the predicate `#delimiter!`.

[torhovland]

Suggested change

	The matched nodes will have a multiline-only delimiter appended to them.
	The matched nodes will have a multi-line-only delimiter appended to them.

[torhovland]

Suggested change

	and prevent the other instruction in the query (the `@append_multiline_delimiter`) to activate. Likewise, if the node is single-line, the delimiter will not be apended either.
	and prevent the other instruction in the query (the `@append_multiline_delimiter`) to activate. Likewise, if the node is single-line, the delimiter will not be appended either.