Provide feedback to users of opt-diff.py, opt-stats.py, and opt-viewer.py,
on how many YAML files have finished being processed, and how many HTML
files have been generated. This feedback is particularly helpful for
opt-viewer.py, which may take a long time to complete when given many
large YAML files as input.
The progress indicators use simple output such as the following:
Reading YAML files... 9 of 1197
Test plan:
Run utils/opt-viewer/opt-*.py on a CentOS and macOS machine, using
Python 3.4 and Python 2.7 respectively, and ensure the output is
formatted well on both.