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/bucket.go

@@ -0,0 +1,47 @@
+package storm
+
+import "github.com/coreos/bbolt"
+
+// CreateBucketIfNotExists creates the bucket below the current node if it doesn't
+// already exist.
+func (n *node) CreateBucketIfNotExists(tx *bolt.Tx, bucket string) (*bolt.Bucket, error) {
+	var b *bolt.Bucket
+	var err error
+
+	bucketNames := append(n.rootBucket, bucket)
+
+	for _, bucketName := range bucketNames {
+		if b != nil {
+			if b, err = b.CreateBucketIfNotExists([]byte(bucketName)); err != nil {
+				return nil, err
+			}
+
+		} else {
+			if b, err = tx.CreateBucketIfNotExists([]byte(bucketName)); err != nil {
+				return nil, err
+			}
+		}
+	}
+
+	return b, nil
+}
+
+// GetBucket returns the given bucket below the current node.
+func (n *node) GetBucket(tx *bolt.Tx, children ...string) *bolt.Bucket {
+	var b *bolt.Bucket
+
+	bucketNames := append(n.rootBucket, children...)
+	for _, bucketName := range bucketNames {
+		if b != nil {
+			if b = b.Bucket([]byte(bucketName)); b == nil {
+				return nil
+			}
+		} else {
+			if b = tx.Bucket([]byte(bucketName)); b == nil {
+				return nil
+			}
+		}
+	}
+
+	return b
+}