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/transaction.go

@@ -0,0 +1,52 @@
+package storm
+
+import "github.com/coreos/bbolt"
+
+// Tx is a transaction.
+type Tx interface {
+	// Commit writes all changes to disk.
+	Commit() error
+
+	// Rollback closes the transaction and ignores all previous updates.
+	Rollback() error
+}
+
+// Begin starts a new transaction.
+func (n node) Begin(writable bool) (Node, error) {
+	var err error
+
+	n.tx, err = n.s.Bolt.Begin(writable)
+	if err != nil {
+		return nil, err
+	}
+
+	return &n, nil
+}
+
+// Rollback closes the transaction and ignores all previous updates.
+func (n *node) Rollback() error {
+	if n.tx == nil {
+		return ErrNotInTransaction
+	}
+
+	err := n.tx.Rollback()
+	if err == bolt.ErrTxClosed {
+		return ErrNotInTransaction
+	}
+
+	return err
+}
+
+// Commit writes all changes to disk.
+func (n *node) Commit() error {
+	if n.tx == nil {
+		return ErrNotInTransaction
+	}
+
+	err := n.tx.Commit()
+	if err == bolt.ErrTxClosed {
+		return ErrNotInTransaction
+	}
+
+	return err
+}