Improved topology LRU cache

[clonker]

• LRU cache now depends on hash over the first MB of data as well as last modified and creation dates.
• began enabling pathlib.Path objects for source/load

fixes issue #1541

[thempel]

looks good to me

[codecov]

Codecov Report

Merging #1545 (f5d0531) into devel (8c2bc84) will decrease coverage by 0.01%.
The diff coverage is 98.36%.

@@            Coverage Diff             @@
##            devel    #1545      +/-   ##
==========================================
- Coverage   92.07%   92.06%   -0.02%     
==========================================
  Files         229      229              
  Lines       26886    26920      +34     
==========================================
+ Hits        24756    24784      +28     
- Misses       2130     2136       +6     

Impacted Files	Coverage Δ
pyemma/coordinates/data/util/traj_info_cache.py	92.41% <83.33%> (-0.60%)	⬇️
pyemma/coordinates/api.py	88.11% <100.00%> (ø)
pyemma/coordinates/data/feature_reader.py	95.60% <100.00%> (+0.10%)	⬆️
...yemma/coordinates/data/featurization/featurizer.py	89.77% <100.00%> (+0.04%)	⬆️
pyemma/coordinates/data/h5_reader.py	96.15% <100.00%> (+0.06%)	⬆️
pyemma/coordinates/data/numpy_filereader.py	96.66% <100.00%> (+0.05%)	⬆️
pyemma/coordinates/data/py_csv_reader.py	87.73% <100.00%> (+0.11%)	⬆️
pyemma/coordinates/data/util/reader_utils.py	88.03% <100.00%> (+0.20%)	⬆️
pyemma/coordinates/tests/test_traj_info_cache.py	98.60% <100.00%> (+0.09%)	⬆️
pyemma/coordinates/util/patches.py	86.40% <100.00%> (+0.06%)	⬆️
... and 2 more

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