Create ~/.ssh/ if missing
Add config for SSH on https port at ssh.github.com

https://help.github.com/articles/using-ssh-over-the-https-port
Add special case for ssh.github.com to connect to port 443 (https port)
instead of SSH standard port.
Add aliases *.ssh.github.com that connect to port 443.
Fixes issue #12.
Update links to Github help pages