BytesIO support

[FoamyGuy]

resolves #51 and originally stemmed from #4831

These changes begin the process of adding support for BytesIO (and possibly other "file-like" objects).

In order to achieve full support for this on modern versions we will need to modify bitmap.readinto() in the core to be able to work with file-like objects.

I was able to successfully test this using the python readinto code from here:

Adafruit_CircuitPython_ImageLoad/adafruit_imageload/bmp/indexed.py

Line 118 in 681a604

else: # use the standard file.readinto

For the purposes of testing I just modified the if statement to force it to use the python readinto code instead of the core bitmaptools.readinto(). My test was run on a FunHouse with 7.0.0-alpha.3 and it did show the downloaded image.

As-is in the core this line ends up raising a TypeError:

https://github.com/adafruit/circuitpython/blob/5f81f9ed1cb9ba98436ebdc54756ef1702681703/shared-bindings/bitmaptools/__init__.c#L479

So for full support we'll need to modify that check and the code that comes after it to be okay with accepting a BytesIO object instead of a file. I poked around with this for a bit, but the C code in question is a bit beyond my capabilities at this point. @jepler I think you may have written this function originally do you have any thoughts on whether it would be possible to modify it to accept BytesIO in addition to file type objects?

[deshipu]

I think the naming here is a bit confusing, because we always have a file in file_or_filename after those lines.
The clean version would be to rename the argument itself to file_or_filename, and then do open_file = open(...) and use open_file everywhere beyond here.