pass generate without writing to store

[Ondřej Synáček]

I'm wondering if it's possible to have `pass generate` just return
the generated password to stdout without providing password name.

The reason is that when I have pass installed on my system, I know
it creates password and would like to use it as password generator
too for other stuff.

Second reason is that I want to write my own wrapper around pass
to augment the functionality and would like to re-use the logic
for generating password. My wrapper would have different way
of creating passwords with custom UI so at some point I only
want to have just the generated password available.