Apply **strong** / *emphasis* syntax for right after punctuations

[KSR-Yasuda]

For strong and emphasis syntax, now it requires line beginning or some space before them.

**strong** aaa **strong**
*emphasis* aaa *emphasis*

Besides these, allow it is placed right after punctuations.

aaa (**strong**)
aaa (*emphasis*)

aaa,**strong**
aaa,*emphasis*

あああ （**最強調**）       # Wide (Japanese) paren
あああ （*強調*）

あああ、**最強調**
あああ、*強調*

あああ　**最強調**          # Wide (Japanese) space
あああ　*強調*

Especially, in Japanese, space is rarely used between words. It is preferred to apply these syntax right after 、 or 。 (Japanese comma, period), even without any space.

[KSR-Yasuda]

At least, Pandoc (v2.17.1.1) considers as I expected.

This avoids things like a clause,* more text

As Pandoc behavior, symbols should be considered as word edge, should not? * occurence in non-symbol characters (e.g. foo*bar), it still treated as the character * itself.

If you want to use * character itself in such edge cases, I think you should escape it as \*.