Pymls

Changed

- Code cleanup
- Many changes over the last minors, a major seemed needed

Changed

- The handling of rigid backing condition has been improved for PEM (the
previous one would give inaccurate results in some cases)

Fixed

- Github-reported security issues in requirements.txt
- Bumped PyYAML version in setup for security reasons (CVE-2017-18342)

Fixed

- Minor bugs and typos in tests and code

Changed

- Some of the parameters set as mandatory for EqF are now optional... as in the
underlying theory

Added

- a DrawsManager class as been added to help with stochastic layers

Changed

- call to `Solver.solve()` leading to a single resultset will return directly this
resultset and not a 1-element list containing it

Added

- the function `Solver.compute_fields()` allows to compute the fields at any interface of
the multilayer
- tests and some documentation
- CI

Fixed

- Dependencies issues