add options and more docstring to loopshapingPI

[baggepinnen]

• Make the plot appear similar to the one produced by loopshapingPID
• Add option to design with filter.

[JuliaControlBot]

This is an automated message.
Plots were compared to references. 9/11 images have changed, see differences below.
After pulling this PR, please update the reference images by creating a PR to ControlExamplePlots.jl here.

Difference	Reference Image	New Image
❌ 0.048
✔️ 0.001
✔️ 0.001
✔️ 0.001
✔️ 0.0
❌ 0.034
❌ 0.059
✔️ 0.0
✔️ 0.01

[codecov]

Codecov Report

Merging #745 (f03fdde) into master (e9460ef) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #745      +/-   ##
==========================================
+ Coverage   91.88%   91.93%   +0.04%     
==========================================
  Files          37       37              
  Lines        3995     4003       +8     
==========================================
+ Hits         3671     3680       +9     
+ Misses        324      323       -1     

Impacted Files	Coverage Δ
src/pid_design.jl	94.68% <100.00%> (+0.14%)	⬆️
src/analysis.jl	96.98% <0.00%> (+0.33%)	⬆️

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