Improve BufferRecyclers configurability via JsonFactory

[cowtowncoder]

(note: offshoot of #833)

While there is JsonFactory.Feature.USE_THREAD_LOCAL_FOR_BUFFER_RECYCLING that allows turning off buffer recycling, there isn't any way to change, for example, default buffer sizes; or logic of what to recycle if anything (current logic will recycle bigger buffers if parser/generator has to realloc bigger ones).
It would be nice to be able to offer alternate configuration, if possible.