Doesn't show states (but shouldn't crash) on old browsers.

- Integrated stex and Markdown mode tests into main test harness

- Added ability to restart tests partway through

- Added verbose option, to add message to output for *every* test

- Added ability to show verbose messages and run specific tests or all tests for 1+ mode(s) via location.hash

- Added support for custom messages (either return value [pass] or throw value [fail])

- Switched away from .innerHTML, .write(), etc in most places

- Make the progress bar actually 0px wide when 0% complete (and still keep padding)

- Added link to tests from each mode's demo page