Added SSH proxy.

* lib/mitmproxy.py: Added ssh related stuff.
* ssh/README: Little info about utility.
* ssh/keys/keygen.sh: Script for generating keys.
* ssh/ssh_proxy.py: SSH proxy utility.
Merge branch 'master' of github.com:saironiq/mitmproxy

My first git conflict solved with Honza's help.

Conflicts:
	lib/mitmproxy.py