My first, simple relx configuration.
Somehow, the .app file escaped inclusion in the git sources up till now.
The sys.config file for the application.
And, a new file for me now: the vm.args file - this specifies Erlang VM runtime parameters.

Both these files are referenced in the relx.config file.
Added the lager parse transform to the compile options.
Introduced overlay behaviour to:
- Create log and config folders in the release.
- Copy the vm.args file from sources to the appropriate release folder.
- Copy sys.config file from sources to the release config folder.