Suite: add #ignore to ignore specs

It replaces a call to #it. Its role overlaps with #skip, but each is
reported in a group in the results:
- #ignore is a spec that should not run
- #skip is a spec which result doesn't matter
Later this can be unified.
Improve results identification

Examples that have more than one result will add only one to the total
count.
Improve reporting Examples' results

- correctly counts Examples;
- report duplicates as errors;
- Suite#ignore'd as skips