`flowAsync` - Githubissues

Long overdue. flowAsync is magical. You can mix and match sync and async, automatically get Promise.all and promiseProps for arrays and objects, and it'll stay sync if nothing is async (e.g. you don't need to await if nothing is async).

flowAsyncDeep is even more magical. It uses the new resolveOnTree method to resolve deep tree structures, so it will work even if you're doing really deep promises (e.g. using an async iteratee in _.update deep in your structure). It's a separate method because traversing the entire object graph is a performance tradeoff we think is worth surfacing to end users. It's possible that we'll deprecate it and make it the default behavior for flowAsync in a future release if the performance hit is generally not noticeable.

Add flowAsync and promiseProps
Add flowAsyncDeep and resolveOnTree
Pass along all tree iteratee props in writeTreeNode (default writeNode for tree maps) and rename interally from writeProperty to writeTreeNode

Resolves #400 and #107

smartprocure / futil-js

`flowAsync` #411