Better docstring linker context inferface

[tristanlatr]

Related to #295, as well as #661 and #662.

This change allow us to output correct link no matter the docstring linker we use to render on what page of the documentation. Historically, the page object was always the one associated with the docstring linker's object (passed on creation), but now we make the differences in between both concepts.

I’ve also totally removed the caching system of xref links. It’s rather complex and it did not improve performance.

[codecov]

Codecov Report

Patch coverage: 94.44% and project coverage change: -0.07 ⚠️

Comparison is base (da6d0d3) 92.47% compared to head (e7644a0) 92.40%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #599      +/-   ##
==========================================
- Coverage   92.47%   92.40%   -0.07%     
==========================================
  Files          47       47              
  Lines        8170     8060     -110     
  Branches     1948     1926      -22     
==========================================
- Hits         7555     7448     -107     
+ Misses        358      357       -1     
+ Partials      257      255       -2     

Impacted Files	Coverage Δ
pydoctor/linker.py	88.13% <93.75%> (-4.41%)	⬇️
pydoctor/epydoc/markup/__init__.py	93.54% <100.00%> (ø)
pydoctor/epydoc2stan.py	94.57% <100.00%> (ø)
pydoctor/model.py	94.56% <100.00%> (ø)
pydoctor/templatewriter/pages/__init__.py	90.69% <100.00%> (ø)

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[tristanlatr]

This is ready to be merged.

[tristanlatr]

I’ll merge this PR, need this to fix other issues.

[tristanlatr]

@adiroiban can I have a approval for this PR since it trashes a lot of the linker code?
This code that was added for the wrong reasons and now it’s best to get rid of it.

[glyph]

This looks… fine, I think… but some of the docstrings and comments need some help.

[tristanlatr]

Hi @glyph, thanks a lot for your review and sorry about the poor quality of the docstrings.

[tristanlatr]

I’ll merge this PR.

[tristanlatr]

We 're good for this PR @glyph

[glyph]

LGTM