* Allow HMX components in markdown
This adds support for HMX components in markdown. The mechanism for importing is via frontmatter. We could do this differently (setup script maybe?) but since this was the easiest to implement I thought it was a good first-pass option.
* Remove node-fetch from snowpack config
* Assert that the runtime is created successfully
* Add back in the micromark extension for encoding entities
* Encode both codeTextData and codeFlowValue
* Install snowpack app's deps
* Add support for React components.
This adds support for react components via a new `extensions` config in astro.config.mjs. In the future we can extend this to do things like look at the import statements, as Snowpack does.
* Fix the tests
