Tfcausalimpact

* Fixed Numpy input bug on array indexes

* Improved unit tests

* Better docstrings for customized models. Updated `getting_started.ipynb` with most up-to-date code.

* Moved CICD to GitHub Actions

* Fixes bug on Python version specification (`3.10.*` is invalid, changes it just to `3.10`).

* Adapt to newer TFP requirements (input time series must have valid frequency).

Fixes bug 17 (Integer columns names)