Support nomnoml for diagrams (see nomnoml.com)

[42sol-eu]

Like mermaid nomnoml is a textbased diagramming processor. I like its very sleekness and the great design.

it is javascript based and should not be hard to integrate.

• sourcecode: https://github.com/skanaar/nomnoml
• electron.io: integration: https://github.com/dqisme/nomnoml-app

integration would be like the mermaid module (code fence with nomnoml)

[abnerlee]

merge into https://github.com/typora/typora-issues/issues/1138