all coqide specific files moved into ide/

lib/interface split into:
 - lib/feedback
     subscribe-based feedback bus (also used by coqidetop)
 - ide/interface
     definition of coqide protocol messages
   lib/pp
     structured info/err/warn messages

lib/serialize split into:
 - lib/serialize
     generic xml serialization (list, pairs, int, loc, ...)
     used by coqide but potentially useful to other interfaces
 - ide/xmlprotocol
     serialization of protocol messages as in ide/interface

the only drawback is that coqidetop needs -thread
and I had to pass that option to all files in ide/