+ 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
The new logo is in the new directory doc/Logos. The old logo has been moved
there too. The documentation has been updated to refer to the new logo.
The new logo was provided in SVG format by Krasimir, but PNG files are included
as well. There are some new rules in doc/Makefile to convert from SVG to PNG,
which you can use if you edit the SVG files.
