Updated README files for exercises (#82)

* Adding initial implementation of basic_encap example

* Updated basic_encap example to count the number of valid packets

* Updated basic_encap example to put encapsulation layer after Ethernet
header.

* Added solution file for basic_encap example

* Changed the name of the basic_encap example to basic_tunnel and called
the new header myTunnel. Also changed the myTunnel field names slightly.

* Updated the README file for the basic_tunnel exercise. Also added topo.pdf
image to serve as a reference during implementation.

* Updated basic/README.md to point to basic_tunnel as the next exercise.

* Updated the README for basic to point to basic_tunnel.

Updated the starter code for basic_tunnel to look like basic
solution with todo comments.

Updated send.py and receive.py to be able to send both plain IP
packets and tunneled IP packets.

Updated basic_tunnel.p4 to have same control flow as p4runtime
exercise.

* Updated the basic and basic_tunnel README files to remove references
to the old run.sh script.

Updated TODO list in basic_tunnel README

* Updated README files to indicate logs are in /tmp

P4D2_2017_Fall/exercises/source_routing/README.md

@@ -123,7 +123,7 @@ There are several ways that problems might manifest:
    Do you have another instance of mininet running? Did the previous
    run of mininet crash?  if yes, check "Cleaning up Mininet" bellow.
 3. `source_routing.p4` compiles but the switch does not process
-   packets in the desired way. The `build/logs/<switch-name>.log`
+   packets in the desired way. The `/tmp/p4s.<switch-name>.log`
    files contain trace messages describing how each switch processes
    each packet. The output is detailed and can help pinpoint logic
    errors in your implementation.  The