imap plan:
 
 flags:
     system flags are described in the imap protocol as 
 words like: \Answered
 the backslash is annoying to type and I think that the 
 text is case insensitive anyway.
 we'll represent these flags by keywords (e.g :answered).
 
 
     
 
 
 todo:
     uid (modifier to copy fetch and store commands)
     
 
 
 search sexpressions (things that can be passwd to the search-mailbox
 function).
 kwda - keywords that don't take any arguments
 kwdb - keywords that do take arguments
 
 
 ssexp :=  nil | ssexp1
 ssexp1 := kwda | (kwdb oprnd+) (and ssexp1*) | (or ssexp1*) | (not ssexp1)
           | set 
 set := number-seq | ( number-seq+ )
 number-seq := integer | (:seq integer integer)
 kwda := :all | :answered ...
 kwdb := :bcc | :before ....
 oprnd := <the appropriate lisp object for the keyword>
 
 
 
 
 
 
 
 
 implemented:
 
   connecting:
     make-imap-connection    
 
   after connecting:
 
     fetch-letter
     mailbox-list
     noop
     search-mailbox
     select-mailbox