PyHDX version 0.4.0 beta3

Changes:

• Refactored config; moved config files, refactored cluster to scheduler_address where applicable (#220)
• Changed Lagrangian squared error reduction from 'total' to 'mean' (affecting regularization values) (#221)
• Regularization components are treated separately and stored in losses dataframe (#222)
• Internal time units are now in seconds (73c387c)
• Added optimization loop callbacks and checkpoint (#222)
• Allow for saving of HDXMeasurementSet objects to .csv/.txt file (9cca09f)
• Allow for reading of 'HDXMeasurementSet` objects from .csv/.txt file (4e9fcac)
• Implemented __str__ for HDXMeassurement objects (5122d23)
• Updated yaml batch formatting format (7d94411, 7c71847)