- this extension is necessary for more generic boundary treatment
- cells can now be structs, i.e. contain different data types
- instead of having numeric index dimensions, one can use the index per cell to adress struct elements

- use data type class consistently instead of strings (in TypedSymbol, Field and jit module)
- new datatype class is based on numpy types with additional specifier information (const and restrict)
- translation between data type class and other modules (numpy, ctypes)

- 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

- windows support
- automatic caching and creation of shared library with all generated kernels
- restrict keyword and function prefixes are preprocessor macros now -> easier to generate one code for linux, cuda, windows

- due to unordered containers  the same method could produce different but functionally equivalent code
- this behaviour is bad for caching

-> switched to ordered containers

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

- check that fixed size kernels are called with arrays of the correct size
- checks that layout of compilation matches runtime layout
- not allowed any more to mix fixed & and variable sized fields in a kernel

- moved simplification strategies from lbmpy to pystencils
- better notebook display for simplification reports
- additional demo and documentation

- version with weights in the entropy denominator

Although expressions have args and function as a tree, args cannot be
modified. So tree-transformations are not possible.
Sympy has subs function, however it replaces all matched in any
subexpression, of the expression (i.e. not only in args but in args args
and so on).