671f8d2 introduced a license header to auto/extract_version.py before the
shebang, causing builds to fail like this:
../subprojects/unity/meson.build:7:0: ERROR: Failed running '/path/to/extract_version.py', binary or interpreter not executable.
The following features from the CMake build have been implemented:
* Library version retrieved from unity.h.
* Extension support.
* Library, header, and package configuration file installation.
This commit is entirely based on existing work by Owen Torres.