Build an API for custom html2text converters

[fs]

Currently I have a small patch that creates a naive html2text converter which strips all tags and removes even the content from some html special tags (like header, script and style). It would be nice to have a documented API where users could plug in their own converter to take advantage of all the modules flying around. Some of these modules are licensed under GPL so TurboMail can't integrate them without loosing its very liberal license.

[amcgregor]

Using the shiny template language standard would be good, too, as having Genshi template messages would be a common usage pattern, and Genshi, at least, can do reasonable down-conversion from HTML to text.