Merge pull request #373 from darribas/master

Merge darribas viz development into PySAL master
shrinking colorbar
Merge pull request #374 from sjsrey/viz

shrinking colorbar
greys for classless map
Adding Baltimore example dataset for use with LM models.
Merge pull request #376 from pedrovma/baltim_data

Adding Baltimore example dataset for use with LM models.
Merge pull request #375 from sjsrey/viz

greys for classless map
Fixing ignorance of argument cmap in base_choropleth_unique
Changing cmap default in plot_choropleth so every type defaults to its own adecuate colormap