Misc. updates

This release includes minor fix and updates to the pipeline. The Cu-Ar (B3000) reference arc file was replaced with a (much!) more accurate version donated by I. Seitenzahl. mpfit was updated to remove some annoying warnings. Same for "header.update" replaced by "header.set".

The installation of the pipeline is now also easier, as the files auto-detect their location. All is required if to add the pywifes folder to the Python path. No need to define any global variable (pywifes_dir) anymore !