[docs] Differentiate Doxygen from LaTeX commands

[ischoegl]

Changes proposed in this pull request

This PR complements #1557, and solely replaces \f[ / \f] / \f$ by @f[ / @f] / @f$. The change clearly differentiates Doxygen commands from $\LaTeX$ commands. In addition, spaces are added to better separate Doxygen from $\LaTeX$ / improve readability.

While the PR creates considerable churn, there will not be a question about what style to follow for Doxygen documentation in the future.

If applicable, fill in the issue number this pull request is fixing

Addresses Cantera/enhancements#179

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Checklist

• The pull request includes a clear description of this code change
• Commit messages have short titles and reference relevant issues
• Build passes (scons build & scons test) and unit tests address code coverage
• Style & formatting of contributed code follows contributing guidelines
• The pull request is ready for review

[speth]

Sadly, separating this from #1557 created some merge conflicts. Can you fix these, @ischoegl, so we can merge this?

[ischoegl]

Rebased. Could you reapprove?