Restructure examples

[matthiasdiener]

• No more -lazy symlinks
• No more -mpi in name (the only non-MPI example, wave.py, has been renamed to wave-nompi.py).
• Test accuracy of all examples, comparing eager/lazy/numpy, as part of run_examples.sh

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Questions for the review:

• [ ] Is the scope and purpose of the PR clear?
  • [ ] The PR should have a description.
  • [ ] The PR should have a guide if needed (e.g., an ordering).
• [ ] Is every top-level method and class documented? Are things that should be documented actually so?
• [ ] Is the interface understandable? (I.e. can someone figure out what stuff does?) Is it well-defined?
• [ ] Does the implementation do what the docstring claims?
• [ ] Is everything that is implemented covered by tests?
• [ ] Do you see any immediate risks or performance disadvantages with the design? Example: what do interface normals attach to?

[majosm]

Closes #393.

[matthiasdiener]

Done in #954.