Refactor docs to use inclusive language.

[bdice]

Description

This PR refactors some language present in the documentation and API of signac to move towards more inclusive documentation.

Motivation and Context

This PR is motivated by discussion at a recent signac developer meeting.

Types of Changes

• Documentation update
• Bug fix
• New feature
• Breaking change¹

¹The change breaks (or has the potential to break) existing functionality.

Checklist:

• I am familiar with the Contributing Guidelines.
• I agree with the terms of the Contributor Agreement.
• My name is on the list of contributors.
• My code follows the code style guideline of this project.
• The changes introduced by this pull request are covered by existing or newly introduced tests.

If necessary:

• I have updated the API documentation as part of the package doc-strings.
• I have created a separate pull request to update the framework documentation on signac-docs and linked it here.
• I have updated the changelog and added all related issue and pull request numbers for future reference (if applicable).

[mikemhenry]

This looks good, later today I'll have more time to double check that we got everything.

[csadorf]

@klywang Do you think you will be able to have a look at this?

[codecov]

Codecov Report

Merging #342 into master will decrease coverage by 0.02%.
The diff coverage is 78.94%.

@@            Coverage Diff             @@
##           master     #342      +/-   ##
==========================================
- Coverage   76.22%   76.19%   -0.03%     
==========================================
  Files          43       43              
  Lines        7096     7104       +8     
==========================================
+ Hits         5409     5413       +4     
- Misses       1687     1691       +4     

Impacted Files	Coverage Δ
signac/contrib/indexing.py	75.35% <75.00%> (-0.25%)	⬇️
signac/contrib/project.py	91.31% <77.77%> (-0.24%)	⬇️
signac/__main__.py	80.04% <100.00%> (ø)
signac/contrib/__init__.py	92.85% <100.00%> (+0.26%)	⬆️

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[klywang]

Everything looks good!