Make a way to parameterize inline tests

Expose extensions and html flags parameters so that tests could specify
what code paths they want to exercise.
Fix bug in isHtmlTag()

Fix what seems to be a typo. j should iterate through all tagname, so it
should be initialized to zero. The test exposes this bug.
Extract repetitive code to a func
Make isHtmlTag() case insensitive
Add an option to strip <script> elements

Partially addresses issue #11.
More <script> stripping

Partially addresses issue #11.
Couple more tests
Add HTML_SKIP_SCRIPT to MarkdownCommon
Fix typo
Improve html element stripping code