changes to eit wave plotting routines. Velocity polyfit is now second order and takes the time information from the unravelled maps in order to make the calculations. Added a width_vs_longitude plotting function to show the width of the wavefront along its length at a given time.
added a base map difference module to eitwaveutils.py
added check of imput file exposure time in data_hough_detect.py. Short exposure frames are removed from the analysis. Added additional argument to main, allowing selection of either running difference or base difference methods.
changed base_diff header information in eitwaveutils.py
Merge pull request #33 from aringlis/master

New plotting routine in eitwaveplot, added base map difference module to eitwaveutils, and tweaks to data_hough_detect