Make the output reproducible

[lamby]

Whilst working on the Reproducible Builds effort [0], we noticed
that pydoctor generates output that is not reproducible.

By iterating over the filesystem (which returns values in a non-
determinstic order) we end up with different id="" attributes in
the HTML.

This affects other packages such as "subvertpy" amongst others.

[0] https://reproducible-builds.org/

[codecov]

Codecov Report

Merging #146 into master will increase coverage by 0.05%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #146      +/-   ##
==========================================
+ Coverage   62.31%   62.36%   +0.05%     
==========================================
  Files          21       20       -1     
  Lines        3375     3372       -3     
  Branches      707      707              
==========================================
  Hits         2103     2103              
+ Misses       1070     1067       -3     
  Partials      202      202

Impacted Files	Coverage Δ
pydoctor/model.py	76.2% <100%> (ø)	⬆️
pydoctor/nevowhtml.py

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[glyph]

Ideally this would come with a change, but it looks like a very straightforward change, and pydoctor doesn't have the greatest coverage to begin with :).

Thanks for this contribution!

[lamby]

@glyph

Ideally this would come with a change,

Hm? :)

[ldanielburr]

@lamby I think @glyph meant to say "Ideally this would come with a test,..."

[lamby]

Ah! Thanks :)

[glyph]

Indeed that is what I meant.