[WIP] Very plain doc conversion for Dash

A very simple script to generate a Kapeli Dash docset.

TODO:

 * [ ] get some feedback
 * [ ] automate submission to https://github.com/Kapeli/Dash-User-Contributions (80% done)
 * [ ] document submission to Dash User Contrib
 * [x] make SQL output in gendocs optional (gendocs --dash)