Implement JavaScript UI for attachments

This one is a bit of a doozy. A summary of the changes:

- Session has grown storage for attachments which have been uploaded but
  not yet sent.
- The list of attachments on a message is refcounted so that we can
  clean up the temporary files only after it's done with - i.e. after
  copying to Sent and after all of the SMTP attempts are done.
- Abandoned attachments are cleared out on process shutdown.

Future work:
- Add a limit to the maximum number of pending attachments the user can
  have in the session.
- Periodically clean out abandoned attachments?

1 files changed, 4 insertions, 0 deletions

diff --git a/server.go b/server.go
index dc2708e..7a82d35 100644
--- a/server.go
+++ b/server.go
@@ -73,6 +73,10 @@ func newServer(e *echo.Echo, options *Options) (*Server, error) {
 	return s, nil
 }
 
+func (s *Server) Close() {
+	s.Sessions.Close()
+}
+
 func parseUpstream(s string) (*url.URL, error) {
 	if !strings.ContainsAny(s, ":/") {
 		// This is a raw domain name, make it an URL with an empty scheme