Sort headers/global definitions to enable reproducible code generation

See merge request pycodegen/pystencils!52

Address #13: Use sympy.codegen.rewriting.optimize

See merge request !34

headers and global_declarations are generated by methods that return
sets. So even with the same inputs it is not guaranteed that the same
source code is generated since sets do not guarantee a specific order
when iterating over them.

AES-NI vectorization improvements

See merge request !46

CI: Add minimal-sympy-master

See merge request !50

Close pystencils' config file after writing

See merge request !51

Actually increment counter inside random_symbol

See merge request !49

Add pyhtml to tests and artifacts

See merge request !41

Fix typo in "pre-push"

See merge request !44

Add PyPI badge

See merge request !45

in unit testing without display plots, the same figure would be used
over and over again. This is problematic when mixing 3D and 2D axes

If this line
from setuptools import find_packages, setup
is run after
from distutils.extension import Extension

a wrong Extension class is used

Basic support for OpenCL (experimental)

See merge request pycodegen/pystencils!29

Fix get_type_of_expression for constants like sympy.pi

See merge request pycodegen/pystencils!35

Problem some constant expressions are neither Float,Integer,Rational but
don't have arguments.

>>> isinstance(pi, Integer)
False
>>> isinstance(pi, Float)
False
>>> isinstance(pi, Rational)
False
>>> pi.args
()

Implement sp.Sum, sp.Product

See merge request !38

Contest: ignore two more files if waLBerla is not available

See merge request pycodegen/pystencils!40

The line is only need when running pytest form the root directory

Pre-push hook

See merge request !36