Add Arbitrary Point Selection, as is done in the Android Version

[mkrupczak3]

To make OpenAthena more useful with object detection and other computer vision integrations, this library should be able to cast a ray towards any pixel in the image (as is possible in the Android version) rather than only the center point.

Relevant PR from the Android version:
Theta-Limited/OpenAthenaAndroid#56

[mkrupczak3]

Here's the relevant issue from the Android version:
Theta-Limited/OpenAthenaAndroid#8