Add bindings for instruction disassembly

[Phantomical]

This is my attempt at wrapping xed_format_generic in an idiomatic wrapper. I'm rather happy with how it turned out.

This PR introduces three function variants to cover the different use cases for xed_format_generic. All three are methods of DecodedInst.

fn disassemble(&self, syntax: Syntax) -> String

This is the simplest one. No configuration, just provide a syntax and get a disassembly string.

fn disassemble_with<F>(&self, options: DisassembleOptions<F>) -> String

More complex. Now you configure it by passing in options. This variant is still infallible so it probably won't work with any complicated disassembly callback. In order to be infallible it requires that the callback's error type is std::convert::Infallible.

fn try_disassemble_with<F>(&self, options: DisassembleOptions<F>) -> Result<String, F::Error>

This one supports the most options. It supports any disassembly callback and takes care of plumbing the error around in the XED callback.

There are a couple of different types that are used as part of this API. I've created a new top-level disassemble module and stuck them in there. It also gives a convenient place to stick some guide level documentation and example on how to use the API.

Other notes

• It's not possible to implement DisassemblyCallback for both FnMut(u64, &mut WriteBuf<'_>) -> Option<u64> and FnMut(u64, &mut WriteBuf<'_>) -> Result<Option<u64>, E>. I've chosen to only implement it for the first one with the idea that actually implementing the trait on a type is less likely to be as much of an issue when the disassembly callback is complicated enough to need to return a result.