Typo's + small corrections/improvements for problem class documentation

[lisawim]

No description provided.

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (6c39f2f) 73.06% compared to head (43c0e22) 73.06%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #358   +/-   ##
=======================================
  Coverage   73.06%   73.06%           
=======================================
  Files         269      269           
  Lines       23044    23044           
=======================================
  Hits        16836    16836           
  Misses       6208     6208           

Files Changed	Coverage Δ
...ns/problem_classes/AcousticAdvection_1D_FD_imex.py	100.00% <ø> (ø)
...oblem_classes/AdvectionDiffusionEquation_1D_FFT.py	0.00% <ø> (ø)
...tations/problem_classes/AdvectionEquation_ND_FD.py	66.66% <ø> (ø)
...implementations/problem_classes/AllenCahn_1D_FD.py	0.00% <ø> (ø)
...implementations/problem_classes/AllenCahn_2D_FD.py	95.28% <ø> (ø)
...ementations/problem_classes/AllenCahn_2D_FD_gpu.py	0.00% <ø> (ø)
...mplementations/problem_classes/AllenCahn_2D_FFT.py	0.00% <ø> (ø)
...mentations/problem_classes/AllenCahn_2D_FFT_gpu.py	0.00% <ø> (ø)
...mplementations/problem_classes/AllenCahn_MPIFFT.py	80.15% <ø> (ø)
...entations/problem_classes/AllenCahn_Temp_MPIFFT.py	81.30% <ø> (ø)
... and 31 more

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