Fix specification of gray level in slider_demo; thanks to Matthias Michler
reverted a bug I introduced when toying around with copy region in agg
added some helper functions for poly collections and masked regions
added save_background.py example.
added more comments.
cosmetic fixes
example showing how to re-use a map background.
added new embedding_map_in_wx.py example, courtesy of Mauro Cavalcanti.
Update sidebar.
added new links to sidebar
