Server.(h|cpp) : abstract server base class
LeafServer.(h|cpp) : subcorpus server, formerly CDDCCorpusListenHost
BranchServer.(h|cpp) : distributed server, formerly CDDCServerListenHost
+ added 'reload' server message
+ unified (leaf|branch) message parsing code and syntax
+ TODO: implement leaf-node commands (get_first_hits, get_hit_strings) for branch-node servers