Fix for all allowed alignment methods

[mfitzp]

This implementation should offer all the same options that exist in the original MATLAB implementation of the algorithm. At present many of the options work, although some combinations have issues. This is an issue to track the progress on implementing anything that does not work but should.

• [x] 'average' target
• [x] 'median' target
• [x] 'max' target
• [x] 'average2' target
• [x] 'average2' multiplier average2_multiplier
• [x] 'max' target
• [x] all above targets with intervals inter=1...inf
• [x] co-shift preprocessing
• [x] co-shift preprocessing with coshift_preprocessing_max_shift
• [x] co-shift preprocessing with intervals (any)
• [x] fill_with_previous=False to use np.inf to fill gaps
• [x] custom scale (in ppm)
• [x] 'n' maximum shift (specified)
• [x] 'b' best maximum shift (search for)
• [x] 'f' fast-search for best maximum shift

[mfitzp]

As far as I can tell the current implementation is complete. Report any failures as separate bugs!