Convert chat log to Fountain tokens.

[louh]

This is stage 1 of turning a Slack message history into tokens. copied from #3:

Convert chat log to Fountain tokens. Fountain.js uses a token structure internally to handle the translation between parsing a Fountain-formatted text file and the HTML view. It is not a public API but because it works, we should steal it. Holding our data state in this token structure allows us to work on it programatically.