Mermaind CLI to Support NEO theme -t "Neo"

[abrahamagc]

Is your feature request related to a problem? Please describe.
Neo theme have made Mermaid look very futuristic and I have started showing to my friends why this product is so cool when using the Neo Editor. Unfortunately Neo theme is not available in CLI. So for folks who want to use CLI we cannot use it.

Describe the solution you'd like
Neo theme to be available in CLI as part of theme -t "neo"

Currently it supports:
-t, --theme [theme] Theme of the chart (choices: "default", "forest", "dark", "neutral", default: "default")

Describe alternatives you've considered
tried to modify theme but could not work it out

Additional context
no additional context - but keep up the good job! Love Mermaid!!!