Embed hexadecimal input data instead of strings

This PR is based on the discussion in #3, and in particular on the ideas of @rolk and @bska therein. It should solve the problem about the compiler complaining about long strings.

This approach increase the memory consumption, so the largest benchmark model is removed.

I would appreciate if someone could test this one, i.e. build it and run `bin/upscale_relperm_benchmark`