Enhance the Lemon parser generator so that it creates a faster parser at the

Enhance the Lemon parser generator so that it creates a faster parser at the
cost of slightly larger parser tables.  Add the ability to measure coverage
of the generated state machine when compiling with the -DYYCONVERGE option.
In SQLite, add the SQLITE_TESTCTRL_PARSER_COVERAGE test-control to query the
new parser coverage feature.