Update documentation

[lgoettgens]

Resolves #123.

I am happy to change anything, if requested.
If someone knows about a package following the best practices described here, I will gladly add it to the list.

[codecov]

Codecov Report

Merging #159 (4ff4da3) into master (94a9c7a) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #159   +/-   ##
=======================================
  Coverage   77.07%   77.07%           
=======================================
  Files          11       11           
  Lines         724      724           
=======================================
  Hits          558      558           
  Misses        166      166           

Flag	Coverage Δ
unittests	77.07% <ø> (ø)

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Impacted Files	Coverage Δ
src/Aqua.jl	73.07% <ø> (ø)

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[lgoettgens]

I furthermore removed a compat info in a docstring for Aqua v0.5. In my opinion, this either belongs to release notes, or should be added similarly everywhere else. This lonely one doesn't make sense to me.

[lgoettgens]

Another slightly larger change: Much content of the README.md has been moved to the documentation. I didn't really like the previous hack to include the README.md as a docstring, and that lead to formatting issues. Now, the README.md is a lot shorter, as everything important has moved to the documentation.
In my opinion, the docs should be the one place where one can find everything.

[fingolfin]

Looks good to me! Just to double check, did you verify that the resulting HTML produced by Documenter looks the way it should / you expect it to look?

[lgoettgens]

Looks good to me! Just to double check, did you verify that the resulting HTML produced by Documenter looks the way it should / you expect it to look?

The doc preview unfortunately does not work since I work on a fork. But my local build looks good.