Implement literal pgn

[lenguyenthanh]

I put it in testKit for now, as I don't see using it in prod. But could be useful for testing.

the usage is in the tests:

  import macros.*
  test("pgn macro"):
    val pgn = pgn"1. e4 e5 2. Nf3 Nc6" // We validate this at compile time.
    assert(pgn.tree.isDefined)
    assertEquals(pgn.toPgn.toString, "1. e4 e5 2. Nf3 Nc6")