Added self-updating, better docker-compose control

* Added --self-update to check for and download new versions of
  the phar
* Added --only option which accepts a comma-separated list of
  services to pass to docker-compose pull/up
* Added --updated option to only pass the updated services to
  docker-compose pull/up

CHANGES

@@ -32,3 +32,12 @@
 
 - Bugfix: The lockfile is no longer removed automatically, but only if it was
   created by the current instance.
+
+**0.1.6**
+
+- Implemented self-updating (use -U or --self-update)
+
+**0.1.7**
+
+- Added `--only` option, to only pull for specific services
+- Added `--updated` option to only pull updated images