Use StrictUndefined for creating jinja2.Environment

See merge request !7

Fix printing of file name in template cpp files

See merge request !6

error occured when using folders that can be accessed with two different paths via symlinks

adapt to new create_staggered_kernel API

See merge request !3

codegen.py fix: bug in the communication of corner directions

See merge request !2

In the function comm_directions the corner directions were treated wrongly.
This fix also generalized comm_directions so it will also work for higher dimensions

- when reading from ghost layers (previously the only option) a pull
  communication is required
- if a kernel writes to the ghost layer a "push" communication has to be
  done
- the new PackInfo generator can now derive push and pull packinfos from
  a given kernel

- 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