Mail proto has subject last; Pack Pascal strings.

The Notification SMS protocol has 00 Sender, Body
The Notification Email protocol has 01 Sender, Body, Subject. These were incorrectly ordered before.
  Retained the logical (displayed) ordering for the caller.
Packing a leading byte for the length followed by the string is effectively packing a pascal string.
Endianness is not important for strings.
Pack 'p' format wants to be told the string length, used a lambda expression to get it right.
Allowed email body length of up to 255 characters. No reason to use unsigned bytes for length.

Remaining issues:
Maxing out all the lengths of the email notification doesn't seem to complete the notification.
  Yet format is 'right' and total is under 4K.
Now playing message was limited to 30 chars.
  Using a 40 40 40 update
  > TrackTrackTrackTrackTrackTrackTrackTrack AlbumAlbumAlbumAlbumAlbumAlbumAlbumAlbum ArtistArtiArtistArtiArtistArtiArtistArti
  generates a correct 30 30 30 message
  >>> 005e0020101e4172746973744172746941727469737441727469417274697374417274691e416c62756d416c62756d416c62756d416c62756d416c62756d416c62756d1e547261636b547261636b547261636b547261636b547261636b547261636b
                ^^ 30                                                         ^^ 30                                                         ^^ 30
  but firmware 1.9.1 shows:
  > ArtistArtiArtistArti-ArtistArtiAlbumAl...
  > TrackTrack-TrackTrack...
  > AlbumAlbumAlb...
  Why is Album munged into Artist? Likely a firmware bug.
Added a playing command to update music data.
pebble.py does nothing when run. Note ID globable.
Turn off protocol debug messages again.
Merge pull request #14 from dlamblin/master

Fix email notifications, disable debug, add now playing command to p.py