Bump Documenter.jl to v1.0

[lgoettgens]

See title.

Documenter.jl v1.0 has a lot more features for cross-referencing between docs of different packages, that can be very useful for our copy-pasting hack. But I skipped dealing with that / deactivated it for now and leave the fix to #588.

Preview: https://docs.oscar-system.org/previews/PR2927/

[codecov]

Codecov Report

Merging #2927 (1a746ee) into master (fe5db32) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #2927      +/-   ##
==========================================
- Coverage   80.40%   80.39%   -0.01%     
==========================================
  Files         461      461              
  Lines       65589    65589              
==========================================
- Hits        52734    52733       -1     
- Misses      12855    12856       +1     

Files	Coverage Δ
...edralGeometry/Polyhedron/standard_constructions.jl	95.65% <ø> (ø)
src/utils/docs.jl	1.33% <0.00%> (ø)

... and 1 file with indirect coverage changes

[lgoettgens]

The warning

┌ Warning: Unexpected Julia interpolation of type Symbol in the Markdown.
│   value = :k_
└ @ Documenter.HTMLWriter ~/.julia/packages/Documenter/cxHBW/src/html/HTMLWriter.jl:2215

will get resolved by thofma/Hecke.jl#1246.

[benlorenz]

The preview looks good, I did not check all the pages but I haven't found any issues.

[HereAround]

Thank you @lgoettgens . Similar to @benlorenz , I checked the preview and could not find issues. I believe this is thus ready to go.