Add -q flag to suppress status output

[martinxsliu]

Hi there!

First of all, thanks for all your efforts in building this great tool!

I'm submitting a PR to add a -q command line flag to hide the status logs it emits when generating fakes. For example,

Writing `FakeFoo` to `path/to/fake_foo.go`... Done

This would reduce the chatter in our build logs and allow us to more easily identify problematic lines.