PEP 518 build isolation fails.

Cython and pysam have to be installed beforehand.

https://github.com/pypa/setuptools/issues/1405#issuecomment-409663455

install.sh

 #!/bin/sh
 /usr/bin/env python3 setup.py build_ext
 # .egg-link does not work with PYTHONPATH ?
-/usr/bin/env python3 -m pip install -e .
-/usr/bin/env python3 -m pip install  --no-deps --ignore-installed .
+# https://github.com/pypa/setuptools/issues/1405#issuecomment-409663455
+/usr/bin/env python3 -m pip install --no-build-isolation -e .
+/usr/bin/env python3 -m pip install --no-build-isolation --no-deps --ignore-installed .