Various updates to noise, xc, response & fsspec codes as well
as many bugfixes (too many to list in detail here so look at
the individual files for those)
- noise codes are likely broken at this point because of new
  additions (noise_c3 in particular)
- xc codes underwent many edits for freq-domain and coherency
- fsspec changes related to backprojection
- response code edits as needed for annotated sacpz files
- bugfixes to changeheader & getheader (of minor concern)
- minor updates elsewhere