Added `parse_headers` method, made backwards-compatible changes to `request` for handling parsed headers (and raise exceptions for unsupported header types).
To use in CircuitPython, simply install the [Adafruit CircuitPython bundle](https://github.com/adafruit/Adafruit_CircuitPython_Bundle).
[Read the docs](https://circuitpython.readthedocs.io/projects/requests/en/latest/) for info on how to use it.