Add printf and fls/fprint* output functions

[cxw42]

In App::GitFind::Actions, implement do_foo() for the following foo: fls, fprint, fprint0, printf, fprintf

[cxw42]

Useful resources: https://perlmaven.com/writing-to-files-with-perl and https://perlmaven.com/printf by Gabor Szabo.