After fixing trivial problem in translator.html, the demo works, but
the example grammar contains only one langauge, so it is not so
interesting. translator.html is located in src/runtime/javascript.
The editor.html in the same location also works.
+ Rename some txt2tags file from .txt to .t2t and remove abandoned .txt files.
+ Add program update_html that finds all .t2t documents and updates the
corresponding .html file. It can be invoked with 'make html'.
+ Add style to some .html documents