Improve RXingResultPoint usage

[Asha20]

Closes #12

[Asha20]

@hschimke I think this might be a good point for a review and maybe a merge if everything looks good. There's still more that can be worked on, but I feel like there's enough improvement here that it's worth merging it and adding more with another PR.

Here's what this PR includes:

• RXingResultPoint is renamed to Point
• MathUtils is completely gone
• Some other duplicated point math functions are gone
• ResultPoint usage across the repo is completely removed (the only reason it's still there is because the proc macro wants it implemented for Point)

[hschimke]

I'll review this evening. For reference: it's just now morning for me.

[hschimke]

This looks great, I passed review, I will merge in the morning. Thanks for your hard work!