Made structural changes in how the opacity is calculated:
Instead of having an set of shifted-profiles (each at the same
resolution of the wavenumber array), I will have two core wavenumber
samplings.  A 'regular' (coarser) one that will have the output
resolution.  A second sampling will be an ovrsampled version (by a
integer factor) of the wavenumber array.  The profiles will be
pre-calculated over this oversampled array.  When calculating the
contribution of each line, the code will dynamically select an
sampling scale for each layer (such that all lines are resolved, at
least).  the dynamic-sampling resolution will be the oversampling
resolution times an integer factor.  The factor will be an exact
divisor of the oversampling factor.  This allows the code to
downsample the array to the regular gridding.
iomisc: Added divisors to find exact divisors of an integer.
numerical: Added integ_trapz for integration and downsample to
  resample down an array.
structures_tr: Added oversampling wavenumber array, and divisors (of
  the oversampling factor).
makesample: Initialize non-oversampled and oversampled arrays.
extinction: Implemented the dynamic-sampling calculation.  Implemented
  getprofile, but it's breaking due to unknown reasons.
slantpath, eclipse: simplyfied the code to calculate the optical depth.  No
  need to be equispaced inpact-parameter anymore.