see changelog

- build_compspec, experimental calculation standard now. Neglect small differences from other version
  old version still available (commented out)
- finished fit_powerlaw_individual
  - added several necessary functions
  - added variable fitting regions, depending on redshift
  - gives much better results than before
  - fixed problem that flux_error_log values much too small
    - problem was that d/dx log10(x) = 1/(x*ln(10))!
- added PyS_SDSS-calc_compspectra
  - program which calculates composite spectra for different redshifts
  - spectra are binned (new composite spectrum added in SDSSclasses!)
  - flux values are summed and at the end normalized by fitted powerlaw
    continuum. Fit is done to actual compspectra
    - new fitting was derived from this
- improved speed of find_element_larger_in_arrays
- probably more