Literate programming

[konnov]

We have been discussing for some time how it could be useful to generate Quint specifications from Markdown. This is especially useful for protocol designers. The workflow would look like follows:

• Write prose in Markdown
• Introduce Quint code snippets in the Markdown document
• Generate Quint code from the Markdown document
• Analyze the Quint specification, edit it
• Update the Markdown document again

The very first prototype of this idea can be found in https://github.com/informalsystems/quint/blob/igor/cosmos-bank/examples/cosmos-bank/cosmos-bank.md

[shonfeder]

See #449