fcs-fit: Fix reduced chi^2
Bump corr
read_photons: Add some basic sanity checks
read_photons: A bit of sad documentation
timetag_parse: Use skip_wraps=1 by default

Not sure why this wasn't the default previously. Regardless, this
eliminates the large timestamp offset that timetag files were seeing.

In principle this shouldn't have affected anything, but unfortunately it
seems this offset upsets favia, resulting in large G(\infnty) values for
reasons I haven't had a chance to investigate.
fcs-corr: Use full correlation function for G

The issue was favia's inability to handle offset timestamps. This should
be fixed in favia but for the moment I've just fixed the cause of the
offset.