Add float support for generate_range()

[aricasas]

It would be cool to add float support to this function. So that we can generate random floats with custom ranges.

Example:

let rng = nanorand::tls_rng();
let rand_num: f64 = rng.generate_range(-3.0..5.5);

[aricasas]

I found how rand implements float ranges, I think, which could be useful:
https://docs.rs/rand/0.8.4/src/rand/distributions/uniform.rs.html#788-997

In essence, they generate a number [0,1), then multiply by the size of the range, and finally add the lower bound. But they also handle a ton of edge cases in their code, so that makes it more complicated.