add api page that everything that is exported

[baggepinnen]

This is quite useful to have and common among other packages. Also serves as a catch-all for stuff we forgot to include

[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
✔️ 0.003
✔️ 0.003
✔️ 0.0
✔️ 0.001
✔️ 0.0
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❌ 0.042
✔️ 0.006
✔️ 0.0

[codecov]

Codecov Report

Merging #613 (659c0e5) into master (094983a) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #613   +/-   ##
=======================================
  Coverage   86.81%   86.81%           
=======================================
  Files          31       31           
  Lines        3239     3239           
=======================================
  Hits         2812     2812           
  Misses        427      427           

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