Py-fparser: python parser for Fortran code (#6794)

* py-fparser: parser for Fortran 77..2003 code

* py-fparser: guard against external pytest.ini

* py-fparser: define 'develop' version as latest master branch

* py-fparser: fetch tagged versions from git repo

* py-fparser: add latest release 0.0.6

* py-fparser: whitespace adjustments for flake8

* py-fparser: inherit python dependency from PythonPackage

* py-fparser: rely on spack to resolve sub-dependencies

* py-fparser: try type='test' for py-pytest

* py-fparser: fetch release tarballs instead of git commits

* py-fparser: test deptype is available, remove comment

* py-fparser: limit versions that use py-six

* py-fparser: version ranges do not need a lower bound