Decouple palette Rgb from Sled

[DavJCosby]

Right now to create a sled, your only option is:

let sled = Sled::new("/path/to/config.toml")?;

Which will populate the Sled struct with LED data, each LED getting 32-bits/channel for color. This behavior should be overridable.

type Rgb8 = Rgb<_, u8>;
type Rgb64 = Rgb<_, u64>;

let lightweight_sled = Sled::<Rgb8>::new("/path/to/config.toml")?; 
let precise_sled = Sled::<Rgb64>::new("/path/to/config.toml")?;

Perhaps even extending to support other palette spaces like RGBA, HSL, etc.

[DavJCosby]

Lets play some more with this idea. If we let the user specify the the data structure they want to use for colors, we can totally drop palette as a dependency altogether. We'd just have to add some trait bounds to make some guarantees.

One for example, we'd probably need T impl Default to allow us to construct generic colors in the first place.

When #26 gets added, that compiler feature would probably add some requirements like T impl std::ops::Mul<f32, Output=T> and t impl std::ops::Add<Output=T> to enable us to blend between colors.

I'll be experimenting with this design on a the decouple_colors branch.

[DavJCosby]

I've got this compiling on the decouple_colors branch. Unit tests don't pass yet as they'll need some rewriting, but this seems to be working!

use palette::rgb::Rgb;
let mut palette_sled = Sled::<Rgb>::new("path/to/config.yap")?;
let mut tuple_sled = Sled::<(u8, u8, u8)>::new("path/to/config.yap")?;

palette_sled.set_all(Rgb::new(1.0, 1.0, 1.0));
tuple_sled.set_at_angle(0.2, (64, 128, 255));

[DavJCosby]

Added bonus, with palette moved from a dependency to a dev dependency, a vanilla build of spatial_led compiles much faster. Goes from 31 dependencies down to 20, compiling on release went from 10.44s down to 3.22s.

[DavJCosby]

Completed by #91