Remove the confusing doc folder

All documentation is in README.md, guide/ and manual/ now.

doc/overview.edoc

@@ -1,4 +0,0 @@
-@author Loïc Hoguin <essen@ninenines.eu>
-@copyright 2011-2012 Loïc Hoguin
-@version HEAD
-@title Socket acceptor pool for TCP protocols.