Revert "Oops: Adding missing header"

This reverts commit 9b4f4c5e8bf47097f12e0485bbe5e729b96f528a.
Revert "Move constants into header file, to allow compiler to do"

This reverts commit 5925efc338cbcb3c5f2fb48ef9675e343442410b.
Turn constant expressions into defines to cope with obsoltete compilers
Merge branch 'constants' of https://github.com/stestagg/bitfield into constants