add -q, --quiet flag to surpress non-error output

[jedahan]

First pass at #46, tests pass and manual testing looked good.

[dbrgn]

Thanks, that was fast :) PR looks good.

The README is missing an update with the new command. Furthermore, I currently prefer if the version bump is only done on release. But I can fix these two issues myself.

Edit: Oh and there was a typo: surpress should be suppress :)

[dbrgn]

One more thing: Could you add a few small tests for this? You can take a look at tests/lib.rs for reference, for example test_missing_cache. Thanks to assert_cli it's very simple to call the binary and to verify the output.

[jedahan]

K, added tests. A bit hacky but seem to work.

[dbrgn]

Nice, thanks @jedahan!

[dbrgn]

Merged in 8784b55.

[dbrgn]

@jedahan Ok, all open pull requests have been merged. I'll leave for 2 weeks of vacation tomorrow, some testing would be welcome during that time. If everything works, I plan to make the next release early October.