PEP 8 Implementation

[razvanhas-plusai]

Describe the bug
py_jama_rest_client.client.JamaClient.__get_all does not follow the PEP 8 Descriptive: Naming Styles convention.

This leads to the problem, that when creating a child class from JamaClient, the __get_all is not available under this name, but rather under _JamaClient__get_all.

As the convention suggests:

single_leading_underscore would be the correct choice: _get_all

Would be great if you could fix this :D