Add a flag so that only classes for which coverage changed are listed

[tm1000]

Fixes #58

[github-actions]

Code Coverage Report

Package	Base Coverage	New Coverage	Difference
functions.ts	🟠 53.16%	🟠 57.14%	🟢 3.98%
reports/clover/index.ts	🟢 100%	🟢 100%	⚪ 0%
reports/clover/parser/index.ts	🟢 84.31%	🟢 84.31%	⚪ 0%
reports/clover/types/index.ts	🟢 100%	🟢 100%	⚪ 0%
reports/cobertura/index.ts	🟢 100%	🟢 100%	⚪ 0%
reports/cobertura/parser/index.ts	🟢 92.31%	🟢 92.31%	⚪ 0%
reports/cobertura/types/index.ts	🟢 100%	🟢 100%	⚪ 0%
utils.ts	🟠 72.96%	🟠 73.31%	🟢 0.35%
Overall Coverage	🟢 70.95%	🟢 71.86%	🟢 0.91%

Minimum allowed coverage is 70%, this run produced 71.86%