v1.7.0

• Added custom sampler feature. Interface requires creation of a class, but allows for inclusion of things like Gibbs samplers. User can explicitly pass in features to the sum-of-squares function.
• Added check routines for reading in parallel MCMC results to ensure only directories with name 'chain_' are queried.
• All files were updated to comply with formatting standards using flake8.
• Added coverage report check to ensure minimal testing requirements are met.
• Added original covariance matrix to results structure for reference.