the idea being a fully modernized version of Sindre's promise-fun package:
- proper module property in package.json for modern bundlers
 - all the promise modules on their own
 - but a single module 'promise-fun' that just exports those, like d3
 - so now you just add promise-fun as a dependency, but then you use whichever piece you need and don't have the whole thing bloating up your bundle size
 - standardized repo layout for each promise module
 - collect it all together into something for https://www.gitbook.com/