Add minor extensions to the process class

[m-cip]

• Add new methods vmin, vmax, vsum, vmean, vvar, vstd to the process class, to perform summary operations across values, for each time point and path.
• Add tests for the interp_kind attribute, and for the no-ovveride commitment of numpy.ndarray methods by the process class.
• Perform minor documentation edits.

[codecov-io]

Codecov Report

Merging #14 into master will increase coverage by 0.05%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #14      +/-   ##
==========================================
+ Coverage   91.58%   91.63%   +0.05%     
==========================================
  Files           7        7              
  Lines        1877     1889      +12     
  Branches      272      272              
==========================================
+ Hits         1719     1731      +12     
  Misses         96       96              
  Partials       62       62

Impacted Files	Coverage Δ
sdepy/infrastructure.py	88.9% <100%> (+0.14%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 7100340...caa2575. Read the comment docs.