Did parseBackticks.
Did parseEntity.
Did parseHtmLTag.
Did parseAutolink.
Cleanup.
Completed conversion to memoized strategy.

Test suite runs, but many failures.
Fixed rewind on parseLabel.

14 test failures now, all with emphasis.  IN most of all of these
cases, the examples in the spec seem to be mistakes, given what
the spec says.

More troubling, performance is down from around 220 to 83.  This
needs investigation.