Scale down the size of Chinese font a little

[borting]

It is better to align the ascender line of English font and Chinese font, so that the typography looks more beautiful. For example, when the English font is set to 12 pt, Chinese can be set to 10 pt. We can achieve this by using the following command:

\setCJKmainfont[Scale=0.85]{AR PL UKai TW} #12 * 0.85 = 10.2

We should check every heading (e.g. Chapter title & Section title) can be applied with this scale setting as well as the fonts used on different OS.