remove assets.rb (deploy:assets:* tasks)

with this commit, following tasks will be removed:
- deploy:assets:cdn_deploy
- deploy:assets:precompile (override for the original capistrano task)

also removing tests associated with this file assets_spec.rb and removing
assets section from README.
bump version to 0.1.0
Merge pull request #23 from PagerDuty/remove-deploy-assets-tasks

remove assets tasks