Do not report rules marked as manual

[j-fuentes]

In some packages, we have rules marked as manual: true.

That was an attempt to have rules that cannot be checked automatically, but require a human to check them manually (see #73).

The problem is that generated reports mark those rules as missing: true, which is true but can be confusing.

We should discuss ways to improve that.

[j-fuentes]

A way to mitigate that problem is to surface the manual: true property on the final report.