Documentation fixes, weights deprecation and linter warnings

[Ddelval]

The following improvements have been made:

• Improve the documentation of centering, components_ and weights
• Mark the weights as deprecated
• Ensure that the code follows pep-8. In particular, starting non-public fields with an underscore

[codecov[bot]]

Codecov Report

Merging #467 (d6d63d8) into develop (f16462a) will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           develop     #467   +/-   ##
========================================
  Coverage    84.84%   84.85%           
========================================
  Files          132      132           
  Lines        10593    10596    +3     
========================================
+ Hits          8988     8991    +3     
  Misses        1605     1605           

Impacted Files	Coverage Δ
skfda/preprocessing/dim_reduction/_fpca.py	91.20% <100.00%> (+0.21%)	:arrow_up:

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