removed debugging from packet_to_pox
fixed bug where incorrectly typed entry placed in all_macs
fixes to gateway and pgateway topos
fixed shift repr
add_link method added
gateway example appears to work for clients + servers <= 9

todos:
- fix for clients + servers <= 255 (set up mac address assignment)
- remove debugging, add topo printing
- test a bunch
cleaned-up and notated gateway transformation / topo setup
cleaned-up gateway example
slight tightening of code for topology transformation
updated README text
renamed shift to move
renamed learning_switch to mac_learner
added tutorial to repo
split gateway abstraction from kitchen sink
removed deprecated composition example
added symlinks to abstraction examples
updated TUTORIAL file
slight tutorial change
additional tutorial improvements
Merge branch 'master' of github.com:frenetic-lang/pyretic into microflows

Conflicts:
	examples/monitor.py
	frenetic/pox_backend.py