use clap for arg parsing in examples 2 and 3

[dave-tucker]

use clap for arg parsing in examples 2 and 3

[Billy99]

@dave-tucker I think this one is obsolete since the code has move to use clap? Or was this one more generic and the idea was to update examples 2 and 3 to get way from something like:

iface = match env::args().nth(1)

in which case the heading should now read: use clap for arg parsing in examples 2 and 3?

[dave-tucker]

@Billy99 yup you are right. updated title to reflect the current state