Insert make_equidistant to interpolate non-equidistant time series

[BjoernLudwigPTB]

Resolve #30 by inserting a function make_equidistant() into tools module as proposed and discussed in the according issue.

[codecov-io]

Codecov Report

Merging #38 into master will increase coverage by 1.38%.
The diff coverage is 65.38%.

@@            Coverage Diff             @@
##           master      #38      +/-   ##
==========================================
+ Coverage   17.04%   18.43%   +1.38%     
==========================================
  Files          16       16              
  Lines        1267     1291      +24     
  Branches      206      210       +4     
==========================================
+ Hits          216      238      +22     
- Misses       1044     1045       +1     
- Partials        7        8       +1

Impacted Files	Coverage Δ
PyDynamic/misc/__init__.py	100% <100%> (ø)	⬆️
PyDynamic/uncertainty/propagate_filter.py	10% <100%> (ø)	⬆️
PyDynamic/misc/testsignals.py	46.15% <100%> (ø)	⬆️
PyDynamic/deconvolution/fit_filter.py	7.97% <100%> (ø)	⬆️
PyDynamic/misc/tools.py	37.97% <60%> (+23.42%)	⬆️

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[mgrub]

We went through all the new code + tests together with @BjoernLudwigPTB and it looks very good.

[scrutinizer-notifier]

The inspection completed: 3 new issues, 12 updated code elements

[BjoernLudwigPTB]

The interpolation with methods next, previous, nearest and linear is finished and well tested in the test suite. Cubic spline interpolation and least-squares are on the list, but will be added at a later time, as well as integrating uncertainty of timestamps.