Extract changelog juicing from spit.clj
Start of publish-s3 task: Wiring & update planning.
Theoretically, publish is done; thumbnail code extracted from spit.clj
Filter changelog by public image IDs.

(Don't try to upload images that haven't been marked public and had
a thumbnail generated.)
Extract and mock-test S3 image upload and deletion.

Fixes deletion key bug.
Add s3_publish_key_prefix option.
Minor doc'ing
Write DB to S3.
Strategy engine
Ignore the :last-log-id of a strategy unless it failed. (Take from DB.)
Thoughts on failure handling
Utility fn for loading config file from REPL
Implement chunked changelog replay. (Works!)
Doc possible errors; check remote state format; fix tests
Merge branch 'strategy-redux'

Conflicts:
	doc/config.md
Fix Markdown in config.md (bullets and code-quotes)