Changed ground to image iteration from Newton's method to bisection (#32)

* Added method to compute viewing pixel from ground point.

* Added new bisection ground to image

* Changed tests to use CSM values instead of ISIS

* Fixed viewing pixel calculations.

* Actually fixed an issue with determining viewing pixel.

* Changed ground to image convergence to use input precision

* Changed line scan test tolerances

* Switch from simple bisection to false position for ground to image.

* Added more documentation to ground to image method