This reverts commit 46f49143.

- stop clang from bitching around due to floating point conversions
- support empty initializer lists (don't print single `,`)

Hotfix! for creation of wrong index when using generate_boundary in 2D

See merge request !3

Only set block_offsets if it is actually needed

See merge request !2

Provide block offsets to generated lattice models

See merge request !1

needed for RNG

- previously a LatticeBoltzmannMethod object was required to generate
  a lattice model for waLBerla
- problem: output fields, smagorinsky, entropic additions are only done
  when coverting the method to a collision rule
- the new interface now takes a collision rule instead of a LB method

to adapt your app have a look at example usage in
walberla/tests/lbm/codegen

they can be changed while the simulation is running

- turned on restrict keyword by default (makes large difference on GPUs)
- smarter block indexing: changing block size depending on domain size
  Example: previously there where (1,1,1) blocks when requested
  block size was (64, 1, 1) and domain size (1, 512, 512), now the
  block size is changed automatically to (1, 64, 1) in this case
- added __lauch_bounds__ to kernels to allow better optimizations from
  the CUDA compiler

- missing pragma once added
- static variable to member in overlap sweep, when called with changing
  block sizes this lead to wrong results

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

- counter-based philox RNG: counter/key is filled with cell coordinate
  and optional external parameters like block position and time step
- works on CPU and GPU - on CPU only for non-vectorized versions

- introduced more flexible "CustomCodeNode" that can inject
  backend-specific hand-written code

- started with generalized free energy formulation

- removed warnings from generated code
- made generated code string deterministic, generating the same twice
  gives binary equally files now

- small (length < 5) arrays with shape and stride information had to be
  memcpy'd to the GPU before every kernel call
- instead of passing the information as arrays, the single elements are
  passed
- leads to more function arguments, but simplifies GPU kernel calls

-> changes in all backends required