Add an unstable job result

Many CI systems, such as Jenkins, can return an 'unstable'[1] result
from a build job.  Interpret a score of 0 as an unstable result and
apply an exclamation icon for that score.

[1] https://wiki.jenkins-ci.org/display/JENKINS/Terminology

Change-Id: I520c7e0d53ee3349fe5e6058a630bd0d91f61a48
6 files changed
tree: 322084ed62361a0c654f608a577d6644928384db
  1. src/
  2. .buckconfig
  3. .gitignore
  4. BUCK
  5. LICENSE