WIP, created files
WIP: Initial version of credentials

Environment and Instance Profile providers.
EnvCredentials: Use the cannonical env variables
Rename 'set' method to 'are_set'
WIP: Integrate the credentials infrastructure with the Caller.
Fix dynamic load of credential provider classes
Fix credentials initialization for Net::AWS::Caller
TYPO: extend -> extends
Post-merge restyle. Change README to give credit
Add dependencies for the paws CLI
Change implementations for cred providers. Test them too