memory store for append/fetch/copy
move server to its own file
add enum dependency
split messageparts
move utilities
add soledadstore class
move parts-related bits to messageparts
pass soledad in initialization for memory messages
debug info
Unset new flag after successful write
flags use the memstore

* add new/dirty deferred dict to notify when written to disk
* fix eventual duplication after copy
* fix flag flickering on first retrieval.
use enums for dict keys
recent-flags use the memory store
handle last_uid property in memory store
fix find_charset rebase
docstring fixes

Also some fixes for None comparisons.
changes file
Fix copy and deletion problems

* reorganize and simplify STORE command processing
* add the notification after the processing of the whole sequence
allow to pass file as argument
Fix UIDVALIDITY command.

thanks to evolution for complaining about this.
Fix indexing error that was rendering attachments unusable

Also, check for empty body-doc
fix badly terminated headers