rewrite gen_range to take any range type instead of low, high

[cyrgani]

This is a breaking change and requires the next released version to be 0.3.0.

This PR rewrites gen_range and gen_range_with_state to take one argument that is any range type (impl RangeBounds<T>) instead of two arguments low and high. It also adds an example to show that all core range types are supported.

This has several advantages:

1. Right now, there is no easy way to get "a random byte" / "a random u8", since quad_rand::gen_range(0, 255) is never going to return 255, as this program demonstrates:

fn main() {
    for _ in 0..1_000_000 {
        let r: u8 = quad_rand::gen_range(0, 255);
        assert!(r != 255);
    }
}

With this PR, one would simply write quad_rand::gen_range(0..=255) (or just quad_rand::gen_range(..) as long as the type of the range elements can be inferred) and get an u8 that can be 255 too.
2. It is currently not always clear to a user whether the high argument is inclusive or exclusive, which has caused confusion and bugs in the past (e.g. #13). The new API solves that problem by making inclusive ranges explicitly low..=high and exclusive ones low..high.

It is also more consistent with other ecosystem crates like rand.

Fixes not-fl3/macroquad#403.