CSS Fixes and Tweaks
- New progress style (which also fixes an alignment issue)
- Fix spacing of `<pre><code>` blocks
- Better looking admonition (that doesn't interfere with other element's styling)
Remove now obsolete admontionicon extension
- admonition icons are now added with pure css
Upgrade PyMdown extensions
- b64: run as a post processor to catch all possible paths
- githubemoji: upgrade to latest (no functional changes)
- headeranchor: Add itself without needing changes to toc extension
- magiclink: Even better regex rules
- tasklist: No functional changes
- progressbar: Now requires title to be quoted (no longer optional).  Inline settings support is removed in favor of using inline attr_list support (new).  Syntax now requires only one equal sign, but can take any number now.  addclasses and levelclass settings renamed to add_classes and level_class.

Related changes:
- toc reverted to its original form as it no longer conflicts with headeranchor
- Update test.md