Tests: Add unit test for unescape.
Lexer: Normalize escaped regexes
Lexer: Remove default DummyLogger.

This reverts commit 14b4b6321cab902a0b844e5f988b76992a9c57f5.

Conflicts:
	error.py
	lexer.py
Lexer, Test: DRY Make explode a lexer builtin.