basic fill_between implemented
Fine tuned how fill_between works

Made changes to better integrate the existing plotting routines with
the fill_between.

* Removed vme_get_avg_scalar_sig_and_band due to redudancy.
* Implemented vme_get_sig_min_and_max to extract sig_min and sig_max from
	the extra infromation.
* Made explicit get function for vme_get_extra_from_data in case I need
	to do something fancy in the future.
Plotting the upper and lower bands integrated.

Fixed various functions so that there is now an optional band parameter.

Successful plot of different gas voltages and their upper & lower limits.
More sophisticated plots of bands around average.

* Implemented feature to plot custom multiple of a band.
* Added code to implement some multiple of the min/max bands.