Re: Add ZSON extension to /contrib/

Hi hackers,

Many thanks for the feedback and all the great suggestions!

I decided to add the patch to the nearest commitfest. You will find it in
the attachment.

Differences from the GitHub version:

- Code formatting changed;
- More comments added to the code;
- SGML documentation added;
- Plus several minor changes;

I very much like the ideas:

- To use varint, as Tomas suggested
- Make dictionaries variable in size
- Somehow avoid calling gettimeofday()
- Improvements by 2ndQuadrant that Andrew named

However, I would like to decompose the task into 1) deciding if the
extension is worth adding to /contrib/ and 2) improving it. Since there are
people who already use ZSON, the extension should be backward-compatible
with the current ZSON format anyway. Also, every improvement deserves its
own discussion, testing, and benchmarking. Thus I believe the suggested
approach will simplify the job for reviewers, and also save us time if the
patch will be declined. If the patch will be accepted, I will be delighted
to submit follow-up patches!

If you have any other ideas on how the extension can be improved in the
future, please don't hesitate to name them in this thread. Also, I would
appreciate some code review.

--
Best regards,
Aleksander Alekseev