Add new utility inverf.pro

Add the inverse error function utility, downloaded from somewhere.  Possibly
useful for speeding up error-bar computation via bootstrap formalisms.
Speed up error-bar computation

Modify the brute-force error bar computation method in
subroutines/omni_compute_ebars.pro to (1) utilize the values of the PDF
itself as the levels for determining area enclosed, and (2) change the FOR
loop over the levels (min -> max) to a WHILE loop (max -> level) to stop
computation when the proper area has been computed.

This removes the NLVS optional input, which requires commensurate changes in
distance_omnibus.pro