Refactor and improve component API with f32 infinities

[Nexfader]

First of all, thanks for the library! I wanted to improve its code quality, so I've decided to open this PR. Here's what I've done:

• Made use of Bevy's Rect, Aabb2d and Rust's Range types to make the code more idiomatic;
• Extracted some logic into separate functions, which reduced code duplication and also will be helpful in unit-testing later;
• Simplified bound handling: it now heavily uses f32::INFINITY and f32::NEG_INFINITY, making calculations seamless and simpler (as opposed to constantly dealing with Options);
• Standardized the usage of vec2 over Vec2::new (previously, the code contained both);
• Changed single to get_single in camera_zoom (similar to what use get_single when getting the window #58 did for camera_movement);
• Reduced if-nesting using if-guards [source];
• Formatted comments according to the style guide.

Sorry if this turned out too opinionated. Feel free to discuss any points in the PR :)

[johanhelsing]

Looks great! Thanks!

I have some trouble understanding that one line, but otherwise this should be ready to merge :)

[johanhelsing]

Awesome. Great work :)