[xExtension-ReadingTime] Reading time of Japanese articles are too short

[hkcomori]

Words counts seem to be incorrect in languages such as Japanese, where words are not separated by spaces.
Therefore, reading time calculated from word counts is very short compared to actual reading time.

I think it is better to calculate the reading time from letters, because it is difficult to accurately count words in these languages.

Therefore, it would be nice to be able to set up the following:

• Source Metrics: Select what to calculate reading time from words, letters. (Default: words)
• Conversion factor: Factor to convert source metrics to reading time. (Default: 300)