Fix #10: Avoid jinja2 dependency

This commit avoid dependency of core pystencils on jinja2.
However this could make the printing of some AST-nodes less elegant.
6 jobs for avoid-jinja2-dependency in 6 minutes and 43 seconds (queued for 18 minutes and 22 seconds)
Status Job ID Name Coverage
  Test
passed #287390
cuda docker
build-documentation

00:00:47

passed #287389
cuda docker
flake8-lint

00:00:17

passed #287388
docker
minimal-conda

00:00:20

passed #287387
docker
minimal-ubuntu

00:00:17

passed #287386
win
minimal-windows

00:01:19

passed #287385
AVX cuda docker
tests-and-coverage

00:03:41