Reorganised functions.py and updated functions.rst

[partben]

Description

Reformatted functions.py so that everything is in alphabetical order, and updated functions.rst so that it includes everything in functions.py.

Fixes #1623

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.

• 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

[brosaplanella]

Hi Bence! Looks good, just see the comment about the duplication. Happy to merge if the tests pass :).

EDIT: Also, can you add a line to the CHANGELOG with the changes you have done?

[partben]

The changelog should now be updated as well.

[codecov]

Codecov Report

Merging #1628 (c3105e3) into develop (00a9357) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##           develop    #1628    +/-   ##
=========================================
  Coverage    99.26%   99.26%            
=========================================
  Files          326      343    +17     
  Lines        18529    18677   +148     
=========================================
+ Hits         18392    18540   +148     
  Misses         137      137            

Impacted Files	Coverage Δ
pybamm/expression_tree/functions.py	100.00% <100.00%> (ø)
pybamm/parameters/parameter_sets.py	100.00% <0.00%> (ø)
...electrolyte_exchange_current_density_ORegan2021.py	100.00% <0.00%> (ø)
...ORegan2021/nmc_LGM50_entropic_change_ORegan2021.py	100.00% <0.00%> (ø)
...c_ORegan2021/nmc_LGM50_heat_capacity_ORegan2021.py	100.00% <0.00%> (ø)
...electrolyte_exchange_current_density_ORegan2021.py	100.00% <0.00%> (ø)
...gan2021/graphite_LGM50_heat_capacity_ORegan2021.py	100.00% <0.00%> (ø)
...n2021/graphite_LGM50_entropic_change_ORegan2021.py	100.00% <0.00%> (ø)
...nmc_ORegan2021/nmc_LGM50_diffusivity_ORegan2021.py	100.00% <0.00%> (ø)
...GM50_ORegan2021/copper_thermal_conductivity_CRC.py	100.00% <0.00%> (ø)
... and 9 more

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[valentinsulzer]

@all-contributors add @partben for docs

[allcontributors]

@tinosulzer

I've put up a pull request to add @partben! 🎉