Default http to port 80, https to port 443.

Hey man - Here's another one.

I found it kinda annoying that I had to include the port number in the URL for http or https web pages, so I modified the link renderer to default http to port 80 and https to port 443, keeping port 70 as the default for any other protocol.

I also added some tests for the new cases.

Mind taking a look? Thanks!