Created Navigator Hybrid Automaton

First attempt at implementing the full navigation automaton. Untested.
Debugged Navigator

navigator.py doesn't crash now, and passes a very simple test.
updated documentation
Obstacle avoidance hybrid working

but there is something very weird about the sonar simulation. The sonar
scans are often misoriented with the map... is this a rounding problem
or something weirder?
update .gitignore
Added DEVNOTES for bug tracking
fix conflicts with fix_sonar branch
Fixed sonar display bug in robot_ha
Merge branch 'solid_walls' into navigator

This merge fixes bugs related to crashing into walls or moving through
walls
Made Robot_HA into subclass of Robot

Now Robot_HA just inherits most methods from Robot. Only the control
policy is different, as Robot_HA must consult its navigation automaton.
wrote simple tests for cross and find_nearest
Added tests for ogmap

I'm using the py.test framework to build tests for ogmap.py, starting
with the simpler operations. Moving forward I need to think of
reasonable unit tests for the more complicated probabilistic operations.
ogmap tests
Adding deterministic robot