- If no saved data exists when loading, a valueerror is now raises. This
  catched that exception to work as expected.

- Adds a filename option for direct loading
- Raise an error if no information given

Adds a lnprob method to a few of the priors. Need to add this for all
priors and a method to calculate it, if not given.

# Conflicts:
#	tupak/__init__.py

If DISPLAY environ not found, then default to the Agg matplotlib
backend. Useful for running on clusters etc.

Moritz Huebner: reintroduced kwargs property/setter, is probably better because that behaviour is getting inherited

See #69

Adds a basic command line interface

Closes #68

See merge request Monash/tupak!40

Adds a basic command line interface

Closes #68

See merge request Monash/tupak!40

Closes #68 by giving a simple interface to set the log-level (unless set
at the script level) and whether or not to use cached data.

Adding cached data check

Closes #64

See merge request Monash/tupak!39