v0.5

Add tupl_dev dir and move codegen & tests there

Focus on simple usage; provide tupl_impl.hpp so no codegen is needed.

The main directory was cluttered with codegen sources and the builds
eagerly ran codegen preprocessing and all tests, unnecessary for use.

Add a tupl_dev directory and move codegen sources and tests there.
A developer can run codegen there to create a tupl_dev/tupl_impl.hpp
that overrides the main directory file.

Remove the CMake developer preset; it only complicates things.