Merge pull request #4 from nssh/master

Plot particles
Only importing proto if it's needed.
Made json default data format.
Moved and refactored get_particle_positions()
Fixed lat/lon noise.
Long line nits.
Better factored bounds checking for course().
Better factored bounds checking for calculating predicted_target_bearing.
Bug fix: Doing deep copy of particle objects during resampling.
Bug fix: Converting result of math.atan2() back to degrees.
Changed default range resolution to 3m and default angular resolution to 1.5 degrees.
Separated trig functions from geo functions.
Added a doc string for get_particle_positions().
Add option for plotting measurements and take care of weights when no measurement
Nits