MEDIUM: map: dynamic manipulation of maps

MEDIUM: map: dynamic manipulation of maps

This patch adds map manipulation commands to the socket interface.

add map <map> <key> <value>
  Add the value <value> in the map <map>, at the entry corresponding to
  the key <key>. This command does not verify if the entry already
  exists.

clear map <map>
  Remove entries from the map <map>

del map <map> <key>
  Delete all the map entries corresponding to the <key> value in the map
  <map>.

set map <map> <key> <value>
  Modify the value corresponding to each key <key> in a map <map>. The
  new value is <value>.

show map [<map>]
  Dump info about map converters. Without argument, the list of all
  available maps are returned. If a <map> is specified, is content is
  dumped.