textproc/py-anymarkup-core: add port: Core library for anymarkup

This is the core library that implements functionality of
https://github.com/bkabrda/anymarkup. You can install this if you only want to
use a subset of anymarkup parsers. For example, you can do this:

$ pip install anymarkup-core PyYAML $ python -c "import anymarkup_core;
print(anymarkup_core.parse('foo: bar'))"

... and you don't need xmltodict installed, for example. You can use anymarkup-
core in the same way you use anymarkup, except you have to import from
anymarkup_core, obviously.

WWW: https://github.com/bkabrda/anymarkup-core

PR: 281219
Reported by: Einar Bjarni Halldórsson <einar@isnic.is> (new maintainer)