Add possibility to define, where downloads are located after build
Now downloads are stored in the folder _downloads. It is hardcoded for example in html builder.
It would be nice to have an option to redefine this location.
It could be done at two levels:
- define the folder name (defaults to _downloads)
- option to define URL root - sometimes downloads are stored in different location than documents - for example in the cloud service (defaults to outdir)
Both values could be redefined in the conf.py of the Sphinx project.