AlFontal/sdcpy: v0.3.0

Drops the usage of Pipenv for python environment management and moves to poetry (closes #6)

Drops the usage of tox and travis to automate the whole CI/CD to Github Actions (closes #5)

Adds support for py3.9, py3.10 and py3.11 (closes #7)

Adds basic testing functionality with pytest and automates the testing with GHA at every push (Adresses #1)

Adresses, in a very hacky way, the problem arising from #4. This can't be considered solved since more careful changes should be made to understand the downstream effects of removing Date indexes in the SDCAnalysis class for the time-series.