Provide a grammar for the list syntax

[ieugen]

Hi,

I've just discovered this app and I'm planning to use it.
One thing that would be nice is to provide a (working !?) grammar for parsing the file.
One option would be Antlr https://github.com/antlr/antlr4 .
This is to ensure that we can generate parsers our of the box and make compatible apps from this.

Having a grammar will allow using a custom list format, suitable for this specific task.
It will also allow building markdown or asciidoc representations (for view only) .

I've noticed #34 and I'm not convinced it is a great idea to force the list format to be markdown compatible.
They kind of serve different purposes IMO.

Some other plain text tools out there: https://plaintextaccounting.org/
A shopping list is a form of accounting (tracking items) and it can be integrated with an accounting software if you start recording pricing and other information.

I am a fan of Asciidoc, which seems to be more extensible than Markdown https://asciidoctor.org/docs/extensions/ https://asciidoctor.org/docs/asciidoc-writers-guide/#lists-lists-lists

and has begun a process of creating a spec inside the Eclipse foundation https://asciidoctor.org/news/2019/01/07/asciidoc-spec-proposal/