Refactor Smile format module use of ThreadLocal to be bound to SmileFactory

[cowtowncoder]

Currently Smile format module uses ThreadLocal for buffer recycling, both for parser and generators. Although eventually it'd be good to make this pluggable, similar to work in jackson-core, it makes sense to start by refactoring to unify handling so it's driven by SmileFactory and not by parser/generator classes.

[cowtowncoder]

Ok, implemented. One less ThreadLocal, things bit more isolated. But the next step is trickier, need to think it through -- ideally jackson-cores BufferRecycler and BufferRecyclerPool could be used somehow but we'll see how that works.