Add vagrantfile + provisioning scripts
Fix #20: use markdown for authors file
Add password flag registration as global option [ref #13]
Update password flag to fetch it's default value from env [ref #13]
Add constants for trousseau password env var name [ref #13]
Update decryption mecanism to use password from global option [ref #13]

This is basically a workaround the global password option system.
A huge refactoring should be made later on to get rid of the whole
environment struct thing.
Update README instructions for password option [fix #13]
Reword password occurences to passphrase
Fix go fmt
Fix #14: password can be retrieved via the system keyring manager
Add Readme instruction to use the keyring manager [ref #14]
Import gpgagent wrapper from camlistore [ref #18]
Fix #18: implement gpg agent support
Add gpg-agent usage instructions to the README [ref #18]
Update README
Replace launchpad goamz with crowdmob's
Refactor s3 enviornment vars handling
Add s3-region flag and enhance region selection
Set remote filename default to trousseau.tsk
Update readme with updated s3 config informations