Cloned originally from https://gitlab.com/jobol/mustach/

Currently tracking upstream release 1.2.10 (2024-10-03).

Changes:
========

Renamed original Makefile to mustach-original-Makefile
and wrote Makefile.am for us.

Added run-original-tests.sh shell script as a wrapper around
mustach-original-Makefile to use the original build process for the test
suite.
