add transient F(t0,tau) file output
This adds two bits of transient output:
- two extra columns for the maximum-likelihood t0,tau values to the standard gridSearch output file, iff a
- one extra file per Doppler candidate with the full t0,tau grid iff a new explicit option
outputTransientFstatMapis set to True.
The main low-level change is that get_fullycoherent_twoF now returns 3 results, two being
None by default except for the transient case, and so I added
 to its calls from other usecases. Tests and examples seem to be unaffected, so I hope I got all of them, but a double-check can't hurt. Or maybe you now a more elegant solution @GregAshton ?