Abstraction Layer for Erlang DS

Erlang DS used to be called “Sigma Proplist” exporting the module pl. Since reworking to ds, this will serve as a backwards compatibility layer for any projects depending on it.

If you are already using sigma_proplist in your projects, you shouldn’t need to make any changes to your rebar.config.

If you’re starting a new project, just use Erlang DS instead.