Lex: Methods should not appear as attributes.
Lex: Drop debugging info; `verbose` should serve only one purpose.
Lex test: Add test for iterator API.
Lex: Simplify iterator API.
Lex: Add quiet_tokenize functionality.
Lex test: Test quiet_tokenize.
Lex test: Separate tests of Lexer class and lex module.
Lex test: Rename `mock` to `logger`.
Lex: Move implementation of tokenize inside Lexer class.
Lex test: Test new tokenize API.
Lex test: Use the new API; return the logger explicitly.
Lex, Lex test: Clear logger status prior to each tokenization.
Lex, Lex test: Fix typos and beautify code.
Lex: Add reset method. Invoke reset method upon data input.

Fix the following bug: After tokenizing a faulty input string,
subsequent tokenizations (of proper input strings) may fail too,
due to the lexing starting from an erroneous state.
Lex: Explicitly bind logger of _LexerFactory to logger of Lexer.

Fix bug where _LexerFactory would receive a None instead of a logger.
Lex test: Test Lexer API separately from Lexer regexps.
Lex: Store debug, optimize and verbose status.
Lex test: [TDD] Expand and groom API testing.
Lex: Improve public API of Lexer.
Lex: Factor inner lexer setup in separate method.