Add PyPI version badge to READMEs.
Apply more review feedback.

- Add docstring to ModelBase.validate_type() function.

- Removed .validate() invocation from parent models.

- Various style and other minor fixes.
Add one more assertion on TestWorkShift.test_is_valid
Delete README.md and keep the .rst one
Make various improvements.

- Add new OptimoValidationError that will be raised for higher-level
  model validation errors.

- Move OptimoError and the new OptimoValidationError to errors.py

- SchedulingInfo model now accepts both string driver ids and Driver
  instances for 'schedled_driver' parameter.

- RoutePlan.validate() now ascertains that every mention of a driver id
  inside a SchedulingInfo object corresponds to a driver in
  RoutePlan.drivers

- Remove references of UnavailableTime objects, as they are simply
  TimeWindow objects.

- Amend tests.
Implement process_optimo_params().

- Implement process_optimo_params() function that ascertains that
  OptimoAPI gets configured correctly.

- Write test cases for process_optimo_params().
Add docstring for process_optimo_params()
Add docstrings to all models and a small fix.

- change Break.start_break and end_break attributes to earliest_start
  and latest_start, respectively.

- Amend tests
Bump version to 0.0.3