Modifed to reflect the rename of the filtering classes
Added a method for checking if the filters are initialized
Basic fleshing out of the KVHDriverNode class which will perform the
work of talking to the sensor andoutputing data to the ROS system.
Fixed rosdoc @file tags not matching their file names
Updated documentation
Created a new class, LinearFilter, which collected the similar code from
the IMUFilter and OdometryFilter classes. Refactored IMUFilter and
OdometryFilter to be children of this new class, to reduce code
reproduction.

closes #3
Fixed the linear array accessors in stateToImu to properly fill the
covariance matrix
Fixed major issue where a virtual methods were being called from the
constructor of LinearFilter. Refactored to take the A, B and H methods
as inputs to the base class, and their child classes now have methods
called at instantiation list time that produce those matricies.
Fixed bug that the indecies for BFL matracies in for-loops were starting
at zero instead of one, causing seg-faults.
Updated update() to account for the various types of update (u+z, z, u,
neither) that are possible
Added many debug messages in an attempt to find the reason for the
segmentation fault that currently happens when an update to the filter
is processed. It's definitely a problem in the actual BFL
filter_->Update() call, which makes it damn difficult to figure out.