- Checks if handlers already exist before adding them
- Add option to turn on/off printing of version information (off by
  default)
- Add call to setup_logger by default (with version information turned
  on by default)

Note - this makes empty calls to setup_logger() obsolete. However, if
you want to log to a file, with setup_logger(label='label') is still
useful.

Docstring update

See merge request Monash/tupak!63

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

Reorganise likelihood and add GaussianLikelihood

See merge request Monash/tupak!65

Attempt to clean up back-end setting

See merge request Monash/tupak!67

Clean up output

See merge request Monash/tupak!66

- Removes warning message
- Add another method to change the backend

Adds a line to print the result and indicate where results are saved

Known interferomters update

See merge request Monash/tupak!64

- Moves the hyperPE likelihood to core
- Adds the GaussianLikelihood
- Update docs
- Update examples