Add flags to miknode_t.

Added flags to miknode_t. Flags are set directly on a miknode with
miknode_set_flags() and miknode_unset_flags(). Each flag is one bit, so we
can have up to 32 separate flags. Each flag has a corresponding MIK_FLAG_*
constant.
Add "no protocol" support.

By setting the MIK_FLAG_NOPROTO flag on a miknode, connections will not use
the Miknet protocol.
Update todo.