Remove circular dependence to bob.extension

Closes #29

See merge request !44

[ci] Try python-only builds

See merge request !43

Pytest

See merge request !41

[script] Revert fixes done to tackle issue #15

See merge request !40

[script] Revert fixes done to tackle issue #24, as https://bugs.python.org/issue30167 is fixed since a couple of years (I cannot reproduce the error anymore on all supported Python versions)

[docs] removing the Local package development for bob and replacing it with a link to bobdevtools

See merge request !36