Support standard normal ~~~mermaid syntax instead of only broken incompatible ~~~mermaid! syntax

[duaneking]

Simply put, this plugin forces people to have to do more work than they should in the name of branding itself, and I see that as hostile to the user. It needs to support "~~~mermaid" as well as its current "~~~mermaid!" for mermaid.

I should not have to maintain or keep multiple versions of markdown files to support the github/mermaid standard "~~~mermaid" syntax and then have to translate or maintain a separate copy of these files just to have the tax use an extra "!" character in this tag as this plugin currently requires based on its docs.

If I create a github markdown file and it includes github standard syntax, using "~~~mermaid" to display something, I currently have to edit that file to make it render in this plugin. That destroys my work, I should not have to change my files like this, I just want one standard format. Let me use github as the standard.

And for context, I'm trying to get mermaid support on gh-pages and this is a breaking bug that helps keep that from happening, based on the little data I have collected. All this plugin needs to do is support both the current ~~~mermaid! syntax and the standard ~~~mermaid syntax github uses.

[qurm]

See my comment on this issue - you can configure this plugin to work with standard syntax, like
```mermaid
I dont really understand why this is not the default configuration.
#70 (comment)

[duaneking]

The proper fix would require that users of GitHub pages not have to do anything, and GitHub simple do the right thing.