Documentation in each `drasil-*` package can “say” more about their interface in their “re-export” file

[balacij]

Each Drasil package has a single “re-export” module exposed in their library (for other packages to have a 'single' import). We can write basic documentation about the usage information of that package in that re-export file to (a) explain the package's exposed functionality and tooling, (b) give highlights and examples of the package, and (c) re-direct to other finer-grain documentation where applicable (such as with Expr -- no need to re-explain each component in the main export file!).

Aeson Example

[daijingz]

Selected this issue and working on it now.