rename [extras] optional dependency to [all]

[AdamOrmondroyd]

Description

Quick one, I find it quite strange we have plural extras but singular test optional dependencies, so I've changed it to tests

To match pandas, rename the optional [extras] requirement to [all].

Checklist:

• I have performed a self-review of my own code
• My code is PEP8 compliant (flake8 anesthetic tests)
• My code contains compliant docstrings (pydocstyle --convention=numpy anesthetic)
• New and existing unit tests pass locally with my changes (python -m pytest)
• I have added tests that prove my fix is effective or that my feature works
• I have appropriately incremented the semantic version number in both README.rst and anesthetic/_version.py

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (ca4e0b2) 100.00% compared to head (29ab7a2) 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #281   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           30        30           
  Lines         2643      2643           
=========================================
  Hits          2643      2643           

Impacted Files	Coverage Δ
anesthetic/_version.py	100.00% <100.00%> (ø)

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[williamjameshandley]

Consistency is important -- I guess the question is whether this should be 'test, extra' or 'tests, extras'. Going by pandas, we should use test, and perhaps all rather than extras

[AdamOrmondroyd]

Ah, I'd misremembered that pandas used [tests]. Now swapped around to use [all]