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/ecn/README.md

@@ -162,12 +162,12 @@ There are several ways that problems might manifest:
    error emitted from the compiler and stop.
 2. `ecn.p4` compiles but does not support the control plane rules in
    the `sX-commands.txt` files that `make` tries to install using
-   the BMv2 CLI.  In this case, `make` will report these errors to
-   `stderr`.  Use these error messages to fix your `ecn.p4`
+   the BMv2 CLI.  In this case, `make` will log the CLI tool output 
+   in th `logs` directory. Use these error messages to fix your `ecn.p4`
    implementation.
 3. `ecn.p4` compiles, and the control plane rules are installed, but
    the switch does not process packets in the desired way.  The
-   `build/logs/<switch-name>.log` files contain trace messages
+   `/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 `build/<switch-name>-<interface-name>.pcap` also contains the