Release Notes Archive Patch

Hi,

Attached is a proposed patch for archiving the release notes on the
website. The patch builds the release note archive without modifying the
schema and works with old and new releases.

It works as such:

- Find all release notes that have been loaded into pgweb (a process
that occurs each release when we load the documentation)
- Find the last modified release notes for each version. This accounts
for the old docs, e.g. there is a copy of the 9.2.8 notes in the 9.3.9
release, so we will render those
- There is a list of all release notes. If you click into it, you will
see the version specific release notes

Known adjustments to be made:

- The URLs on each release note page are broken. I have to figure out
how the best way to change the relative path in the URLs that are on the
page as it is going from the page root (/docs/release) instead of the
site root. This _should_ be easy
- Even with above fix, some URLs will be broken in them, i.e. references
to other release notes
- PostgreSQL v1 + v0: I need to relabel this for Postgres95
- Also, some of the earlier versions do not have the proper release
numbering (e.g. 1.03)

I'm hoping we can put this out with the upcoming release, but am ok with
doing this shortly thereafter.

Comments on patch and approach welcome.

Thanks,

Jonathan