Add devel/py-antlr4-python2-runtime: ANother Tool for Language Recognition (python2 runtime)

ANTLR (ANother Tool for Language Recognition) is a powerful parser generator for
reading, processing, executing, or translating structured text or binary files.
It's widely used to build languages, tools, and frameworks. From a grammar,
ANTLR generates a parser that can build and walk parse trees.

This port provides the python2 runtime.

WWW: http://www.antlr.org/

Approved by: antoine
Differential Revision: https://reviews.freebsd.org/D18631