Add version switch

[jftuga]

You should consider adding a -v switch that will output the program's version and GitHub URL. Right now, there is no easy way to tell which version of up I am running or where I might download a new version. While up is a great program name, it does make it a bit hard to perform a web search for since it is such a generic word. Sometimes -v is used for verbose, but since you already have a -dbg option, I think it would be OK to use -v for version information.

Example:

$ up -v
up v1.2.1
https://github.com/jesusprubio/up