为 Hexo 添加 Mermaid 图表功能

graph TD;
    A-->B;
    A-->C;
    B-->D;
    C-->D;

sequenceDiagram
    participant Alice
    participant Bob
    Alice->>John: Hello John, how are you?
    loop Healthcheck
        John->>John: Fight against hypochondria
    end
    Note right of John: Rational thoughts 
prevail...
    John-->>Alice: Great!
    John->>Bob: How about you?
    Bob-->>John: Jolly good!

gantt
dateFormat  YYYY-MM-DD
title Adding GANTT diagram to mermaid

section A section
Completed task            :done,    des1, 2014-01-06,2014-01-08
Active task               :active,  des2, 2014-01-09, 3d
Future task               :         des3, after des2, 5d
Future task2               :         des4, after des3, 5d

gitGraph:
options
{
    "nodeSpacing": 150,
    "nodeRadius": 10
}
end
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