Added support for HTML-comments, sub- and superscripted text and upper c...

- Added support for upper case, lower case and mixed case tags (by conversion to lowercase before comparing with switch/case).
- Added support for sub- and superscripted text
- Added support for HTML-comments

Also got the PDF-conversion (pdflatex filename.tex) to work but only from command line. Don't know why but it wont work when I put the command in the script.