fix tests. fixes #10

Make tests run on Darwin as well as Linux.

Also update tests to test current behavior of the buildpack
and the correct Go version.
parameterize
write an empty release
write .profile.d/go.sh with path augmentation
Add heroku build constraint
Update echo as well
Update heroku command in README
Make example output accurate
Document the heroku build constraint
update doc links and sample output
missed a doc link
Go 1.1
Merge from kr buildpack
Update revel test app (not actually run)