Methods for line measurements

[ThoChat]

This is a remake of the old PR from Christian Hirt implemented following the current structure of PedPy documentation.

[codecov]

Codecov Report

Attention: Patch coverage is 61.33333% with 58 lines in your changes missing coverage. Please review.

Project coverage is 63.35%. Comparing base (0fd1969) to head (5139677).
Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
pedpy/plotting/plotting.py	8.00%	46 Missing ⚠️
pedpy/methods/flow_calculator.py	73.33%	4 Missing ⚠️
pedpy/methods/speed_calculator.py	82.60%	4 Missing ⚠️
pedpy/methods/method_utils.py	92.68%	3 Missing ⚠️
pedpy/methods/density_calculator.py	88.88%	1 Missing ⚠️

@@            Coverage Diff             @@
##             main     #393      +/-   ##
==========================================
+ Coverage   63.22%   63.35%   +0.13%     
==========================================
  Files          14       14              
  Lines        1357     1501     +144     
==========================================
+ Hits          858      951      +93     
- Misses        499      550      +51     

Files with missing lines	Coverage Δ
pedpy/__init__.py	90.00% <100.00%> (ø)
pedpy/column_identifier.py	100.00% <100.00%> (ø)
pedpy/data/geometry.py	91.90% <100.00%> (+0.19%)	⬆️
pedpy/methods/density_calculator.py	97.50% <88.88%> (-2.50%)	⬇️
pedpy/methods/method_utils.py	82.66% <92.68%> (+1.98%)	⬆️
pedpy/methods/flow_calculator.py	91.30% <73.33%> (-8.70%)	⬇️
pedpy/methods/speed_calculator.py	94.44% <82.60%> (+8.44%)	⬆️
pedpy/plotting/plotting.py	11.62% <8.00%> (-0.54%)	⬇️