Handle HTTP errors and content type better

[makermelissa]

Fixes #37.

Summary of changes:

• It handles HTTP errors by outputting the error code and message and returning.
• Content type is detected as either text, json, and image and is handled better in that manner.
• This also handles the breaking changes between Requests 1.6.0 and 1.7.0 (see Breaking change in 1.7.0: Header keys are now capitalized Adafruit_CircuitPython_Requests#40 for more details).
• Fake Requests was updated to be more like MatrixPortal, but should basically function the same.

Tested on CircuitPython 6 Beta 2 with latest bundle.

[FoamyGuy]

I tested these changes with PyPortal Adafruit CircuitPython 6.0.0-beta.2 on 2020-10-05; Adafruit PyPortal with samd51j20

I tested text with the simpletest script in examples, and json with the quotes script. I also checked a few HTTP errors using a local web server, those are printing nicely.

I have been unsuccessful testing the images so far, but I think I may not be understanding how to use it properly. I'm going to try poking around some other projects later today to see if I can figure that out.

[makermelissa]

Thanks @FoamyGuy. Yeah, images isn't working with version 1.7.x of Requests at the moment. I have an issue open for that at adafruit/Adafruit_CircuitPython_Requests#41. Also, this has a temporary fix in place for adafruit/Adafruit_CircuitPython_Requests#40, but after it's fixed, I may go back and undo the change. However, this does accomplish the original goal of handling errors and content type better.