[tests] write initial unit tests

[signebedi]

Write some basic unit tests for config, context, tagging, and gptty.

[signebedi]

[tests] integrate with testing CI/CD software
We should consider bootstrapping this package to CI/CD software like Travis CI

[signebedi]

[tests] Add context.py tests when model_type == 'v1/chat/completions'
We only have basic context.py tests that don't check for more complex context structures. We should add additional tests when model_type == 'v1/chat/completions'.

[signebedi]

[tests] consider whether and how to test main.py and gptty.py
Currently, we are testing a number of functions, but not testing main.py and gptty.py. These are mostly click interfaces and gptty-specific functions. Is it worth testing these? If so, how?