for some of these files this is needed to make to keep it compiling
after the next patch because the new ErrorMacros.hpp file will no
longer implicitly includes <iostream>. for the remaining files it is
just good style.
While at it, the includes for most of these files have been ordered in
order of decreasing abstraction level.
The functions of linInt.hpp are now used everywhere, but:
- linInt.hpp -> linearInterpolation.hpp (better name)
- linearInterpolationExtrap() -> linearInterpolation() (extrapolate by default)
