FIX: Change strings with invalid escapes to raw strings

[larsoner]

Fixes:

invalid escape sequence \*

[effigies]

Thanks. I've seen that popping up in a lot of projects lately. Is that the only one we have in nibabel?

[codecov]

Codecov Report

Merging #826 into master will decrease coverage by 0.15%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #826      +/-   ##
==========================================
- Coverage    90.1%   89.94%   -0.16%     
==========================================
  Files          96       96              
  Lines       11910    11910              
  Branches     2125     2125              
==========================================
- Hits        10731    10712      -19     
- Misses        834      847      +13     
- Partials      345      351       +6

Impacted Files	Coverage Δ
nibabel/openers.py	94.89% <ø> (ø)	⬆️
nibabel/pydicom_compat.py	77.27% <0%> (-22.73%)	⬇️
nibabel/environment.py	75% <0%> (-20%)	⬇️
nibabel/__init__.py	89.28% <0%> (-3.58%)	⬇️
nibabel/casting.py	84.68% <0%> (-0.86%)	⬇️
nibabel/viewers.py	95.39% <0%> (-0.66%)	⬇️
nibabel/dft.py	80.36% <0%> (-0.62%)	⬇️
nibabel/nifti1.py	91.14% <0%> (-0.31%)	⬇️

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[larsoner]

Found a bunch more and pushed. This at least allows me to run MNE-Python test suite without errors (so far, at least I can collect the tests now!)