This restructuring allows for easier separation of modules into
separate repositories later. Also, now pip install with repo url can be
used.

The setup.py files have also been updated to correctly reference each
other. Module versions are not extracted from git state

- new functions to easily extract stencil coefficients and visualize them
- Moved stencil functions from lbmpy to pystencils

- test run again
- notebooks not yet

- assignment collection
- sympyextensions

- switched to google style docstrings
- removed dead code
- started to annotate types

- if moments have been passed in polynomial, not expanded form to
  computeContinuousMoments (or also cumulants) the results have been
  wrong.
- in practice that affected orthogonalized MRT models

- getShearRelaxationRate is a free function now -> works also with cumulant methods
- better error message when calling kernels with wrong or too few parameters
- entropic & incompressible is not working by default due to pdf shift -> added NotImplemented exception
- new creation function for 'raw_mrt' where all relaxation rates can be independently specified
- enhanced entropic creation funtion, supports omega output field now

Michael Kuron authored Feb 13, 2017 and Martin Bauer committed Feb 13, 2017

This commit makes the Python code backwards compatible down to Python 2.7. Previously it would only run on Python 3.5 and up.

Problems fixed included:
- `time.perf_counter()` doesn't exist
- all classes need to be new-style
- `functools.lru_cache` doesn't exist
- only the last argument to a function call can be `*`-expanded
- the `nonlocal` keyword doesn't exist
- metaclasses are used with a different syntax
- `yield from` doesn't exist
- `tempdir.TemporaryDirectory` doesn't exist
- iterators need a `next()` method

Martin Bauer authored Dec 27, 2016 and Martin Bauer committed Feb 09, 2017

- all functions of these components tested & documented
- various fixes
  - cuda tests only run if pycuda available
  - added missing dependencies to Dockerfile

- possbility for custom ast nodes (debugging)
- support for fields in boundary condition

- wrote a new, separate lattice model for cumulants
- tested with 2D LDC

+ debug nodes in AST
+ continuous moment function now also supports polynomial formulation

- MRT support ( equivalence tested)
- optional replacement of relaxation rates before compilation
- removed very expensive simplify in lbm equation generation (not really necessary)