Draft block interface for SBJson
Update DisplayPretty example to use ARC
Update TweetStream example to use the block interface
Add ErrorHandler block
Rename StreamParser to LowLevelParser and make the stream parser adapter the "real" parser

Rather than having to configure a parser + adapter, you now just configure a
parser; internally this will delegate to a low-level parser.

Rename lots of other classes for clarity.
Rename stream writer to chunk writer too
fixup! Update TweetStream example to use the block interface