Clean multipatch domain

[yguclu]

Require orientation of interfaces (ornt parameter) between patches in a multipatch domain when:

• Creating an Interface object (from sympde.topology.basic)
• Creating a Domain object (from sympde.topology.domain) using either join or from_file constructors

Moreover:

• Make Connectivity.todict() store the orientation in the output dictionary, hence allowing Domain.export() to save that information to file
• Add consistency checks when creating a MappedDomain object (from sympde.topology.mapping)
• Clean up sympde.expr.evaluation and expand its docstrings
• Clean up unit tests after changes:
  • sympde.expr.tests.test_expr
  • sympde.topology.tests.test_logical_expr
  • sympde.topology.tests.test_topology
• Update library version to 0.20.0