Merge pull request #88 from skuschel/albn/dev

Axis:

    * islinear(): changed check to work with axes that have very large numbers (e.g. omega)

Field:

   * add .conj()
    * transform(): enforce broadcasting for transformations that do not broadcast all coordinates
    * _apply_linear_phase(): refactored

helper:

    * kspace_propagate(): refactored and lots of improvements