Update documentation to match current capability and usage.

doc/index.rst:
Add new models to documentation (minus-z is not mentioned except when showing command output since it will be removed in the future).
Show current output from commands used in examples.
Update code exampes to reflect current usage.
Update images.

doc/constraints.png:
Update with more recent version.

doc/dwells_2011_month.png:
Removed file, to be replaced in a separate commit.

examples/plot_by_month.py:
Update code to reflect current models and usage.
Call functions explicitly from matplotlib.pyplot so this example can be run from outside of ipython.

pyger/pyger.py:
Update merge_dwells1 function defaults to reflect common current usage, and to be consistent with documentation.




Signed-off-by: Matthew Dahmer <matthew.dahmer@gmail.com>