Mermaid Mode

Introduction of Mermaid

See [mermaid](http://knsv.github.io/mermaid/#mermaid) for introduction and examples of mermaid.  

mermaid-mode

Emacs major mode to edit mermaid, following features included:

- Auto indentation
- Keywords highlighting
- Compilation and view of document

Feedback

Do not hesitate to send me suggestions or pull requests.