adds stub rake task
retrieve pivotal project data

A nice hash, each key is a project ID and the value contains the
corresponding api token to use.
adds pivotal-tracker

Uses remote git because of non-merged fix for issue.
Implements fetching of metrics for all projects.

Relies on two environment variables, not available on
travis just yet.
updates .travis.yml configuration

* Add secure environment variables for tests.
* Test against ruby-2.0.0 instead of ruby-head.
Use secure travis env vars properly.
Merge pull request #2 from kabisaict/import_from_pt

Rake task to sync with Pivotal Tracker