Finally fixed ASTNode#map and ASTNode#map!.  I will probably still add something to the documentation recommending the use of Visitors instead of the map methods.
Told git to ignore all *.tbl files.  Added a `use` argument to the Brainfuck parser, as well as the infix, postfix, and refix parsers.  Changed the Kazoo parsers to use the 1.9 hash argument syntax.
Issue #17 was caused by only creating shallow copies of the output stack when spliting the parse stack during the parsing of an ambiguous string in an abmiguous grammar.  A deeper copy
is now performed, which should avoid this issue.  A new test case (tc_parser.rb / test_ambiguous_parse_stack) has been added to make sure it doesn't happen again.

Also fixed a typo in the documentation in ast.rb.