Better EPFD Support

[harrison-caudill]

As defined by 47 CFR Part 25 Section 103, include appropriate computations for EPFD for compliance reports.

https://www.law.cornell.edu/cfr/text/47/25.103

[harrison-caudill]

def _gso_victim_epfd(model):
    # http://famille.philippe.gerard.pagesperso-orange.fr/EPFD%20concept/Epfd%20conceptVfinale.htm
    # https://www.law.cornell.edu/cfr/text/47/25.208
    #
    # EPFD is, essentially, the PFD that would be required at the
    # victim's peak-gain angle to produce the same received power as
    # the sum of transmitters.
    #
    # We assume a single contributor, so:
    # Pr = pfd * Ar = epfd * Ar_max
    # epfd = pfd * Ar / Ar_max
    #
    # In log units:
    # epfd = pfd + Ar - Ar_max
    #
    # Alternatively, we can apply a correction term to the pfd
    # epfd_delta = Ar - Ar_max
    pass