hmtx optimization over the Google Fonts collection

I did a test run of hmtx optimization over the Google Fonts collection and
thought the results might be of interest. A few key results:

   - Of 1754 font files, 80.4% (1411) got smaller, 16.4% (288) had no
   change, and 3.1% (55) got larger.
   - For fonts with savings, average was 466 bytes or 1.08% of size
      - Across all fonts, average was 368 bytes or 0.86% of size

Cheers, Rod S.

Per-font results can be seen in
https://docs.google.com/spreadsheets/d/1dgL-il6fIHaHJghlzXz7aM_HEtes9G7Pt7TsnlsxsGc/edit?usp=sharing
.