Speed improvements when loading Piksi format files.
Fix bug in run.py when tracking longer than 37 seconds.
Use cPickle and the latest protocol for speed.

Pickle navigation results in run.py.
TODO: Implement pickling of navigation solution class to do this properly.
Precompute the PRNs for WAAS and other non-GPS constellation satellites.
Switch to using libswiftnav tracking loop filters.
Run C/N0 estimator whilst tracking and save to tracking results.