Reorganize log proccess for download stats

The overall design is to make it easy to have a daily stats file
and an all.edn file with combined stats in the :stats-dir.

To process a log file:
  lein trampoline run -m clojars.stats.process < logfile > day.edn
or
  java -cp clojars-version-standalone.jar clojure.core -m clojars.stats.process < logfile > day.edn

To merge stats together
  lein trampoline run -m clojars.stats.merge logfile1 logfile2 .. logfileN > all.edn
or
  java -cp clojars-version-standalone.jar clojure.core -m clojars.stats.merge logfile1 logfile2 .. logfileN > all.edn

It would be useful to have a cron job that processes the day's logs,
merges with all.edn to a tempfile, and then moves the tempfile back to all.edn
Release 0.13.4
Fix tests & Release 0.13.5
Show download count on artifact page

Fixes #26
Release 0.13.6
Attempt to verify signature multiple keys

The PGP string can encode multiple keys.  Lets try and if any
of them can verify the signature.

Fixes #130.
Release 0.13.7