Add support for S3 through the REST API

This is currently using the old S3 authentication
(https://s3.amazonaws.com/doc/s3-developer-guide/RESTAuthentication.html),
in order to support Exoscale Storage

Refs #112

liquor-cabinet.rb

@@ -5,6 +5,7 @@ require "sinatra/base"
 require 'sinatra/config_file'
 require "sinatra/reloader"
 require "remote_storage/swift"
+require "remote_storage/s3_rest"
 
 class LiquorCabinet < Sinatra::Base
 
@@ -130,6 +131,8 @@ class LiquorCabinet < Sinatra::Base
     @storage ||= begin
       if settings.respond_to? :swift
         RemoteStorage::Swift.new(settings, self)
+      elsif settings.respond_to? :s3
+        RemoteStorage::S3Rest.new(settings, self)
       else
         puts <<-EOF
 You need to set one storage backend in your config.yml file.