FIX: doc-searching

[TTsangSC]

Closes #292.

This PR implements the proposed fixes in the issue, attempting to fix the search function in the docs based on readthedocs/sphinx_rtd_theme#1448 and the associated thread:

• docs/source/cont.py:
  sphinxcontrib.jquery is added as a Sphinx extension so there is a search to fall back on; this also allows for searches to work on local doc builds.
• requirements/docs.txt:
  Bumped sphinx_rtd_theme to a version (1.2.1) containing the linked PR fixing the issue.
• .readthedocs.yml:
  Bumped the build environment (Docker image and Python version) to something reasonably new but not bleeding-edge.

[Theelx]

Along with this PR, since it's a documentation issue: can you move the CHANGELOG.rst entry for #380 from the section under 5.0.0 to 5.0.1? #380 wasn't part of 5.0.0 at its release, and we can't modify existing releases. It'd be useful if you insert it in between the existing ENH and FIX boundary, because keeping the enhancements grouped together and fixes grouped together makes it easier for people to read the CHANGELOG.

[TTsangSC]

Ah yep I messed up, I thought I placed that under 5.0.1 already. Thanks for the heads up!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.13%. Comparing base (60e928f) to head (60aa93b).
⚠️ Report is 13 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #384      +/-   ##
==========================================
+ Coverage   87.56%   88.13%   +0.56%     
==========================================
  Files          18       20       +2     
  Lines        1641     1921     +280     
  Branches      348      412      +64     
==========================================
+ Hits         1437     1693     +256     
- Misses        149      168      +19     
- Partials       55       60       +5     

see 1 file with indirect coverage changes

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[Erotemic]

Excellent, adding this into xcookie will fix search in all my respos. Thanks!

[Erotemic]

The RTD are so much nicer now: https://kernprof.readthedocs.io/en/latest/index.html

Somehow that also gave us a usable sidebar.

[TTsangSC]

Just noticed (since we're working on IPython stuff in #383) that the doc page for line_profiler.ipython_extension is not currently built; we probably need to update .readthedocs.yml so that IPython is installed when RTD builds the docs. Will write a PR for that.