First split into crockery init and crockery run

The init command creates a crockery.db file containing the domain name and
TLS keypair. The run command starts IMAP and SMTP services based on that file.

Supporting only a single domain is starting to look a bit unnecessary. We'll
see how that goes.

vendor/github.com/asdine/storm/index/errors.go

@@ -0,0 +1,14 @@
+package index
+
+import "errors"
+
+var (
+	// ErrNotFound is returned when the specified record is not saved in the bucket.
+	ErrNotFound = errors.New("not found")
+
+	// ErrAlreadyExists is returned uses when trying to set an existing value on a field that has a unique index.
+	ErrAlreadyExists = errors.New("already exists")
+
+	// ErrNilParam is returned when the specified param is expected to be not nil.
+	ErrNilParam = errors.New("param must not be nil")
+)