missing/outdated crate documentation

[letmejustputthishere]

• romans blog, the crate docs and the examples are not in sync. this is mainly around the fact that StableBTreeMap does not require devs to specify a bound anymore
• there aren't examples for how to use the library except for StableMinHeap and StableBTreeMap
• StableVec requiresBound::Bound , which is not documented and compiles, but throws runtime errors
• more docs and examples around schema upgrades and what pitfalls to avoid

[michael-weigelt]

[ ] Mention that MemoryManager should be instantiated only once unless you know that you are doing (TM)

[letmejustputthishere]

in general, i think both the DX and docs could be improved. this is a crate that is heavily used, but not very accessible IMO.

IIRC @keplervital has some tooling that would improve DX, like a storable macro and wrappers around the StableBTreeMap that provide indices and other convenient functionalities