Fixes to MLJ parts of document strings

[ablaom]

NB. The target branch of this PR is dev and not the default branch.

This PR makes some minor editorial fixes to the docstrings. I have only reviewed the MLJ parts of these strings.

Closes #145.

A more substantial issue not addressed here is cross-referenced below.

To do:

• Determine if issue below requires further changes here.

[codecov-commenter]

Codecov Report

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The diff coverage is n/a.

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  Coverage       ?   49.17%           
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  Files          ?       17           
  Lines          ?     1279           
  Branches       ?        0           
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  Hits           ?      629           
  Misses         ?      650           
  Partials       ?        0           

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