Add `history` option to disable GC
Add `history` option to disable GC

For #183

Accepting suggestions for a better name than `history` :-) I picked this
because it tells the Parser to keep around "historical" table columns. So.
*shrug*

This gets awkward, because Parser can now be initialised four ways:

    Parser(Grammar)
    Parser(ParserRules, ParserStart)
    Parser(Grammar, options)
    Parser(ParserRules, ParserStart, options)

Hardmath123/nearley,Hardmath123/nearley,tjvr/nearley,tjvr/nearley