Issue 869 search

[rtimms]

Description

Adds a search functionailty to pybamm.FuzzyDict so that users can search ParameterValues and model.variables

Fixes #869

Type of change

Please add a line in the relevant section of CHANGELOG.md to document the change (include PR #) - note reverse order of PR #s. If necessary, also add to the list of breaking changes.

• New feature (non-breaking change which adds functionality)
• Optimization (back-end change that speeds up the code)
• Bug fix (non-breaking change which fixes an issue)

Key checklist:

• No style issues: $ flake8
• All tests pass: $ python run-tests.py --unit
• The documentation builds: $ cd docs and then $ make clean; make html

You can run all three at once, using $ python run-tests.py --quick.

Further checks:

• Code is commented, particularly in hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[codecov]

Codecov Report

Merging #875 into develop will increase coverage by <.01%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           develop     #875      +/-   ##
===========================================
+ Coverage    97.75%   97.75%   +<.01%     
===========================================
  Files          202      202              
  Lines        10459    10475      +16     
===========================================
+ Hits         10224    10240      +16     
  Misses         235      235

Impacted Files	Coverage Δ
pybamm/parameters/parameter_values.py	100% <100%> (ø)	⬆️
pybamm/util.py	97.7% <100%> (+0.27%)	⬆️

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[valentinsulzer]

looks good to me, thanks!