add mermaid support & 修复regex问题

[Weidows]

[Weidows]

```mermaid
pie
  title Key elements in Product X
  "Calcium" : 42.96
  "Potassium" : 50.05
  "Magnesium" : 10.01
  "Iron" : 5
```


{% mermaid %}
pie
  title Key elements in Product X
  "Calcium" : 42.96
  "Potassium" : 50.05
  "Magnesium" : 10.01
  "Iron" : 5
{% endmermaid %}

本地测试了下前者的写法非常方便,可以被editor识别渲染 The former is very convenient to write and can be recognized by the editor

原始tag写法就不行 The original tag doesn't work

[Weidows]

#3 修复了regex问题