Use @autodocs to dynamically include all docstrings

[JoshuaLampert]

• By using @autodocs we don't need to manually list all definitions with docstring. This means that, e.g., in Use a new DifferentiationMethod type for specifying derivative methods #122 we don't need to change the docs, but the new docstrings are found automatically.
• Added docstrings for spezializations into new section of the API reference. For this I unified the docstrings for BezierCurve because otherwise they would appear three times, which would be redundant,
• Added some links and cross references.

[JoshuaLampert]

What about the specializations? Currently, they are not included in the API list in the docs. I would suggest to add a new subsection ### Specializations under ## Integrals, where we dynamically include all files in the folder specializations.

[github-actions]

Benchmark Results

	main	c64b30a...	main/c64b30a4a2574a...
Differentials/Differential	0.763 ± 0.065 μs	0.766 ± 0.066 μs	0.996
Differentials/Jacobian	0.68 ± 0.026 μs	0.685 ± 0.025 μs	0.992
Integrals/Meshes.Segment/Scalar GaussKronrod	4.42 ± 0.22 μs	4.4 ± 0.22 μs	1
Integrals/Meshes.Segment/Scalar GaussLegendre	0.0741 ± 0.00043 ms	0.0742 ± 0.00052 ms	0.998
Integrals/Meshes.Segment/Scalar HAdaptiveCubature	7.97 ± 0.031 μs	7.96 ± 0.051 μs	1
Integrals/Meshes.Segment/Vector GaussKronrod	6.68 ± 0.083 μs	6.61 ± 0.085 μs	1.01
Integrals/Meshes.Segment/Vector GaussLegendre	0.0891 ± 0.003 ms	0.0871 ± 0.00086 ms	1.02
Integrals/Meshes.Segment/Vector HAdaptiveCubature	10.9 ± 0.31 μs	10.9 ± 0.25 μs	1
Integrals/Meshes.Sphere/Scalar GaussKronrod	0.194 ± 0.00056 ms	0.193 ± 0.00046 ms	1
Integrals/Meshes.Sphere/Scalar GaussLegendre	16.5 ± 1.2 ms	16.5 ± 1.2 ms	1.01
Integrals/Meshes.Sphere/Scalar HAdaptiveCubature	0.19 ± 0.0019 ms	0.19 ± 0.002 ms	1
Integrals/Meshes.Sphere/Vector GaussKronrod	0.231 ms	0.232 ms	0.994
Integrals/Meshes.Sphere/Vector GaussLegendre	19.2 ± 0.45 ms	19.5 ± 0.54 ms	0.987
Integrals/Meshes.Sphere/Vector HAdaptiveCubature	0.255 ± 0.0057 ms	0.255 ± 0.0062 ms	0.998
time_to_load	1.58 ± 0.023 s	1.57 ± 0.0075 s	1

Benchmark Plots

A plot of the benchmark results have been uploaded as an artifact to the workflow run for this PR.
Go to "Actions"->"Benchmark a pull request"->[the most recent run]->"Artifacts" (at the bottom).

[JoshuaLampert]

What about the specializations? Currently, they are not included in the API list in the docs. I would suggest to add a new subsection ### Specializations under ## Integrals, where we dynamically include all files in the folder specializations.

I just did that. What do you think, @mikeingold?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.75%. Comparing base (879b238) to head (c64b30a).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #123   +/-   ##
=======================================
  Coverage   95.75%   95.75%           
=======================================
  Files          17       17           
  Lines         259      259           
=======================================
  Hits          248      248           
  Misses         11       11           

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[mikeingold]

LGTM! Nice work.

Makes progress on #62