numerics/: Remove USE_CLN stuff

There is no need for it.
numerics.cpp: mk_xk_uk() cleans the low-level calculation
numerics/Makefile: CLeanup and small fixes
numerics.cpp: Print additional info to the plotfile
numerics/: Cleanup/change dtau dependency and termination
numerics/.gitignore: Added
make.sh: Bild on ait501

The Makefiles are also affected.
numerics: Terminate at minimal x1
functions.cpp: Add functions cc(t,r) and dd(t,r)
.gitignore: Ignore .tex files!!!!
numerics: Separate into single.exe
numerics/misclib: Created for miscellaneous functions
numerics.cpp: Declare internal functions static
single.cpp: Slightly better variable dtau
single.cpp: Even more better, ha
spectrum.cpp: Generate a crude spectrum on the photon's path
spectrum.cpp: Correct spectrum from stationary source
single.cpp: Handle emin and emax better for spectrum
kerr-newman.metric: Simplify
spectrum.cpp: Use a narrower spectrum