New feature - to_img, makes truncated .img files :)

[sneakers-the-rat]

Also: Features:

• Added ReadHeaderException, raised when header cannot be read with a little more information than the IndexError raised currently
• Uses ReadHeaderException to also better detect another kind of currently unhandled end of recording exception
• Automatically switch to using correct file extension in to_video
• Additional wirefree_battery_sample.img file to test different formats

Bugfixes:

• When returning with headers, data was incorrectly assigned to "frame" rather than "data", dropping it. Fixed.

[sneakers-the-rat]

I'm gonna bypass the review requirement here just bc this is so old and we should get it over with - doesn't affect any shared code

[t-sasatani]

My bad I completely forgot about this and the other PR.