HTML <table> cleanup

* Now, HTML <table> structures in passage text will have all invalid
elements removed - that is, non-table-related elements outside of
<tr>,<th>,<col>,<caption> and <figcaption> elements. Note: this doesn't
work in IE 8 simply because inserting HTML <table> elements doesn't work
in IE 8. For maximum compatibility, use the TiddlyWiki table syntax.
* Fixed a syntax highlighter bug where the final trailing symbol of
certain style syntax wasn't being coloured.