Text fallback when building python API

[q-posev]

• Fix pip installation without HDF5 installed. #123

[q-posev]

Took advantage and fixed a few bugs, cleaned a little bit and improved the build script. Now it copies and uses config.h to build Python API when using make python-install. When building from Python dist tarball (pip install .) - it will try to detect HDF5 using env variables, so they need to be either set in advance or pkg-config will try to find HDF5 and then if both fail - use text.

I also refactored the Python tests, now they can run using pytest parametrization for both HDF5 and TEXT back ends.