Add Mamiya::Storages::Filesystem
Update example
Require villein v0.5.0
Agent#trigger: send event serially
task[_labels] limits task targets by agent labels

- Agent: include LabelMatcher for #match? method
AgentMonitor#statuses(labels:) to filter by labels
String matches Symbol, Symbol matches String
Add Configuration#packages_dir, prereleases_dir
Add Mamiya::Agent::Tasks::Prepare
Agent: support prepare task

- Agent#task_queue: accept Prepare task
- Actions#.prepare: enqueue Prepare task
- Master::Web: prepare API
Adjust dependency loop
Pass logger
XXX: