Core: initial implementation of red-black tree

Signed-off-by: Eduardo Silva <edsiper@gmail.com>
Core: add mk_rbtree.c and mk_rbtree.h

Signed-off-by: Eduardo Silva <edsiper@gmail.com>
Merge commit 'fed3d4224cdbf2fed51c272dde6138df14916aad' into red-black-tree
Configure: link to mk_rbtree.o object

Signed-off-by: Eduardo Silva <edsiper@gmail.com>
Epoll: remove instance field from epoll state nodes and code cleanups

Signed-off-by: Eduardo Silva <edsiper@gmail.com>
Scheduler: use red-black tree algorithm to handle connection nodes

This patch replace the linear query over the busy queue to lookup
connection nodes by a red-black tree algorithm. This represents
a huge improvement in performance under a high load.

Signed-off-by: Eduardo Silva <edsiper@gmail.com>