Add flags to miknode_t and mikpeer_t.

Added flags to miknode_t and mikpeer_t. Flags are set directly on a miknode
with miknode_set_flags() and miknode_unset_flags(). Flags are copied onto
a mikpeer when it is created. 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.