Feature: CI with GitHub actions

[Moritz-Alexander-Kern]

Continuous Integration with GitHub Actions (Travis ⟶ GitHub actions)

In this workflow several runners are setup to run tests on elephant.

Many ideas from the old Travis CI workflow have been recycled to create the following runners:

1. build-and-test-pip

• OS: Ubuntu
• Python: [3.6, 3.7, 3.8, 3.9]
• pip install requirements, (requirements-tests.txt, requirements.txt, requirements-extras.txt)
• pip install -e .
• test with pytest

Runners:

• build-and-test-pip (3.6, ubuntu-latest)
• build-and-test-pip (3.7, ubuntu-latest)
• build-and-test-pip (3.8, ubuntu-latest)
• build-and-test-pip (3.9, ubuntu-latest)

2. test-conda

• OS: Ubuntu
• Python: [3.9]
• install conda enviroment using enviroment-tests.yml
• pytest

Runners:

• test-conda (ubuntu-latest)

3. test-pip

• OS: Windows
• Python: [3.8]
• pip install requirements (requirements-tests.txt, requirements.txt, requirements-extras.txt)
• pip install -e .
• test with pytest

Runners:

• test-pip (3.8, windows-latest)

4. test-pip-MPI:

• OS: Ubuntu
• Python: [3.6]
• pip install requirements (requirements-tests.txt, requirements.txt, requirements-extras.txt)
• pip install -e .
• test with pytest (for MPI use: mpiexec -n 1 python -m mpi4py -m pytest --cov_elephant)

Runners:

• test-pip-MPI (3.6, ubuntu-latest)

5. docs:

• OS: Ubuntu, Python: [3.9]
• install openmpi
• pip install requirements (requirements-docs.txt, requirements-tutorials.txt)
• install conda enviroment using enviroment-docs.yml
• install pandoc with conda
• make html

Runners:

• docs (ubuntu-latest)

• change link to status badge in README.md (current: INM-6/elephant)

• restructure environment.yml, separate environment files for tests and building docs

• add specific triggers to run different tests, i.e. do not run all tests on "PR open"

• remove Travis (.travis.yml and requirements/environment.yml)

[coveralls]

Coverage remained the same at 88.615% when pulling 21f6d77 on INM-6:feature/github_actions_CI into d0d3920 on NeuralEnsemble:master.