Split out code into many crates.

[tkaitchuck]

Right now the crate provides a great way to parse json. But a lot of the simd tricks are much more general. For example parsing a float or an integer from a string, locating unescaped quotes, etc. may be valuable generally.

If these could be made into sub-crates that are individually pushed to crates.io they could be more easily reused in other contexts.

If they can be made nostd perhaps simd parsing of ints/floats could even be added to the standard library instead of the .parse() method on string.

[Licenser]

That's a great idea!

[Licenser]

Not done but the relevant traits now live in value-trait

[Licenser]

we have split things out to the point where it makes sense now