First pass at prose documentation.
Add code examples for proposed API.
Finish documentation, using sketch of final implementation.
Implement task serialization TDD.
News entry.
Bytes, not unicode.
Get rid of tildes because they would have broken sort order.

E.g. "/1/30" is smaller than "/1/3~1", so the order between those two
would be swapped.
More useful demonstration of cross-process tracing, by highlighting
debugging ability.
One more explanation.
Link to relevant docs in news entry.
Add cross-process tracing to introduction.
Missing words.
Address review comment: Better function name.
Address review comment: Better file names.
Address review comment: Explain how to run examples.
Merge pull request #128 from ClusterHQ/cross-process-34

Cross process task tracing.

Fixes #34.