implemented tables
resolved issue with escaped pipes
corrected some omitted characters needing escape in _split_on_unescaped
added tolerance for up to three spaces for headers and first horizontal rule as per markdown extra
added some tests for tables
added reference to new tests
Fix broken escaping introduected in 404344f

`this` is the main markdown object, not the dialect inline itself.
Style change - move function just used in table processing into Maruku.block.table
Implement tables for Maruku dialect by redsun82