Bump minimum required `tasty` version

In `tasty` 0.8 test exceptions are included in result tests. This means
there is no need now to handle a exception status separately.
Add dummy test example that uses `htmlRunner`
Set basic structure of HTML
First attempt to render HTML instead of XML

It typechecks but the example output only shows a failed summary.
The attributes and tag elements will probably have to be modified to
match bootstrap-tree.

See #1.
Remove `xml` dependency
Add last step to render tests

The HTML output doesn't come up properly though.
Cosmetic
Render test summary

The HTML is incorrect but the test results come up. Now it's a matter of
arranging the render steps it properly.
Remove `Debug.Trace`
Nest testcase elements properly under testgroups
Remove summaryErrors
Cosmetic
Extend example test
Clean up generated HTML

It now looks good enough to close #1.
Include bootstrap-tree resources in HTML report

The CSS attributes have to still match.
Make draft bootstrap tree and give different batches to successful/failed tests

There are still several rendering glitches to improve from here.
Fix HTML tree rendering
Restructure summary status area and style up a bit.