Under certain conditions, `howSimilarString` could reach a divide-by-
zero situation which causes bogus values to print in the cache potential
column of the template hints output. This situation essentially causes
a `int(math.NaN())` value to be returned and hilarity ensues thereafter.
This commit adds a "cache potential" column when running `hugo --templateMetrics --templateMetricsHints`.
This is only calculated when `--templateMetricsHints` is set, as these calculations has an negative effect on the other timings.
This gives a value for partials only, and is a number between 0-100 that indicates if `partial` can be replaced with `partialCached`.
100 means that all execution of the same partial resulted in the same output.
You should do some manual research before going "all cache".
