added basic support for hdr, Works On My Machine

[hwangeug]

Did some basic testing with my HDR setup, and found that the screenshot had a peak brightness of 144, so the THRESH_BINARY_INV filter was obliterating everything. Added:

• Linear tone mapping via cv2.normalize if "HDR Mode" is enabled
• Flag in config.txt to enable HDR Mode (looks for hdr=True)
• Hotkey to enable/disable HDR Mode, and save out to config
• Indicator text to show that the program is operating in HDR Mode (so that players don't accidentally miss the DAY text due to not having HDR Mode enabled)

I don't know that 200 is still going to be an appropriate cutoff for THRESH_BINARY_INV - it might depend on your setup, or what else is on the screen, I'm not sure - but it worked for me every time in my limited testing.