Switch to a pallet-repl release.
Use predefined providers in ~/.pallet/

To use a predefined provider, you still need to specify the type of
provider at bootstrap, e.g. (bootstrap :ec2 :provider
:my-ec2-provider), where :ec2 is the type, and :provider is the key
for the :my-ec2-provider that should be present in ~/.pallet .
Allow switching providers.
Provide a meaningful message when bootstrapping EC2.
Update README for release.
Release 1.0-beta.1
Merge branch 'release/1.0-beta.1' into develop