[O] org-sparse-tree by dates range (was: [DEV] Package org-find-timestamps on worg)

[Bastien]

Hi Marc-Oliver,

thanks to the ideas you mentioned long ago for org-find-timestamps.el,
I implemented a new org-sparse-tree possibility: by date range.

Just try `C-c / D' in an Org file and you'll see it.

Thanks again for this idea!

-- 
 Bastien