Keep it Simple

- Removed the additional customisation features `$normalizer-html-font-family`, `$normalizer-h1-font-size`, `$normalizer-h1-margin` and `$normalizer-small-font-size` to comply with the primary goal of normalizer.scss to allow the reduction of the rules load ( which already is minimal ) in the final `CSS` output file.
- Removed the respective customised tests.
- Updated the documentation to reduce duplication of the headers.

Signed-off-by: Stefano F. Rausch <developer@stefano.rausch-e.net>