Support newer Python versions

[ErikBjare]

There seems to be a lot of issues when installing on other Python versions than 3.7, since I have a pretty extensive history of battling issues like these I thought I might give it a shot (especially now that we have a CI pipeline).

Documenting known issues here:

• Installing pywinhook on Windows on Python 3.9 requires extra build deps (swig, VS C++ tools) due to no prebuilt wheels being available on PyPI
  • Fixed by referencing wheels built elsewhere in requirements.txt
• Build errors for numpy/pandas
  • It seems this is merely due to the versions in requirements.txt being old. Using newer versions works just fine. (another reason for build: moved to pyproject.toml/poetry #22)
• tables 3.6.1 has no wheels available for Python 3.9 on platforms other than Linux (see: https://github.com/NeuroTechX/eeg-notebooks/actions/runs/400623523)

[JohnGriffiths]

We'll aim to address newer Python version support with high priority.

However, it is quite tricky to make quick progress on as we need to co-ordinate multiple people with access to different OSs etc.
(as we observed at the Dec brainhack)

[JohnGriffiths]

Related: #29