Add setting to allow HTML

[yhatt]

It is good to be togglable enable or disable HTML as a configuration of extension. It would work as same as --html option in Marp CLI.

Feedbacked to #4 (comment).

[yhatt]

An updated VS Code 1.32 is no longer required reload when installing Marp for VS Code. But internally, it means that adding toggleable settings based on an unique Marp instance become be harder.

I have to re-think a logic to toggle HTML by setting, and Marp Core may require update.

[yhatt]

Shipped with v0.0.6 🚢

[eric-burel]

That's a great feature, could you add a line about this option in the Readme?
It's very hard to find doc about HTML support in Markdown, either in Marp or with other tools. It's usually supported but it's not always obvious, I had to dig until I found this issue.

Or maybe the fact that HTML is supported should be specified in Marpit doc directly?

[yhatt]

You're right. Inspite of my fault, I got tired to response troubles caused by missed writing this documentation.

Continue in #98.