Closing various issues

Closes #140, #139, and #137

See merge request Monash/tupak!119

Clean up of setup

Closes #146

See merge request Monash/tupak!117

Closes #141

Closes #141

See merge request Monash/tupak!112

The attempt to capture git version information is not much more robust.
If any error is raised, the error is printed, but won't break the
install. This means if, for example, git it not installed then it will
still work.

Resolve "Use of `scipy.special._ufuncs.i0e`"

Closes #149

See merge request Monash/tupak!116

Various improvements to the GaussianLikelihood

See merge request Monash/tupak!115

keys() now returns a dict_keys object which is a view. So when the
actual keys are updated, so is this, but we do not want that behaviour.

1) If sigma is not given, then it will not be sampled over (or a warning
raised that you didn't specify a prior for sigma).
2) Comments added to explain the logic throughout
3) Tests added for the Gaussian likelihood

Hyper fix

See merge request Monash/tupak!114

Warnings cleanup

See merge request Monash/tupak!106

# Conflicts:
#	tupak/gw/conversion.py
#	tupak/gw/detector.py
#	tupak/gw/likelihood.py

Previously, the frequency_array was passed to infft, but it should
instead be the sampling frequency.

Implements automated burn-in cuts for emcee