v0.0.30

• Thanks to hpoul the XML library now works with both beta and stable flutter channels.
• Thanks to hydeparkk encoded mailbox paths are now used in copy, move, status and append
• Fix decoding message date headers
• Fix handling mailboxes with a space in their path
• Allow to easly serialize and deserialize MailAccount to/from JSON.
• Extended high level MailClient API:
  • Allow to select mailbox by path
  • Disconnect to close connections
  • Include fetching message flags when fetching messages
  • Allow to store message flags, e.g. mark as read
  • Provide access to low level API from within the high level API