Print a URL to a GitHub repository or source file.
$ ghurl
https://github.com/attente/ghurl/tree/f590f24d888edcf4fee641799ffd2091c518dbbf
$ ghurl ghurl 17
https://github.com/attente/ghurl/blob/f590f24d888edcf4fee641799ffd2091c518dbbf/ghurl#L17