Allow line weights to be floats

[Keavon]

We currently are using u32 line weights because f32 and f64 don't implement std::hash::Hash which is needed for the options bar UI widgets.

Hint: a starting point for going at this issue is searching the project for "Weight" (in quotes), changing is_integer: false to true, and then trying to go replace all the u32 instances with f32 and f64. We probably want to stick with u64 for the UI widgets and then maybe use f32 for line weights or maybe switch that all over to f64 also. The hard part is finding a solution to the Hash trait, since oddly floats in Rust don't implement it.

[0HyperCube]

@Keavon We don't actually need the hash trait any more. Just remove the derive from the __OptionsUpdate enum.