retransmissions, acknowledgements, and queued receives now all work. FUCK YES!

(also some minor adjustments to logging and the build system)
renamed sn_txrx.h to sn_packet.h
first implementation of routing is done. only does dumb tree-routing for the moment.
routing appears to work

Test cases run (using routeleaftest):
1. Tree = Coord(0x0000)-Router(0x2000)-Leaf(0x2001); traffic 0x2001<->0x0000. Works.
2. Tree = Leaf(0x0001)-Coord(0x0000)-Router(0x2000); traffic 0x2000<->0x0001. Routing works, but causes assertion failure in do_security_checks. An assertion failure that should be impossible.

Test cases to run:
* Tree = Leaf1-Coord-Router-Leaf2; traffic Leaf1<->Leaf2.
* Tree = Leaf1-Coord-Router-Leaf2; traffic Leaf1<->Router.
* Tree = Coord-Router[1-3]; traffic RouterX<->RouterY