Add follow uri

Another enhancement: when on a line that contains a uri, press `g` and it will start the `goto.rb` hook with the uri that it could parse.

Here's a sample, working hook:
```rb
system.exec("xdg-open #{uri} > /dev/null")
```

I'd like to add some smarter uri detection (ie multiline, before and after the current line, http(s) only) before merging though.