Some documentation fixes

[dabail10]

1. Remove the Tahoma font as this makes the equations too big.

2. Remove some occurrences of the string "\_" that was rendered in the documentation.

• Developer(s): D. Bailey

• Please suggest code Pull Request reviewers in the column at right.

• Are the code changes bit for bit, different at roundoff level, or more substantial? BFB

• Please include the link to test results or paste the summary block from the bottom of the testing output below.

• Does this PR create or have dependencies on Icepack or any other models? N

• Is the documentation being updated with this PR? (Y/N) Y
  If not, does the documentation need to be updated separately at a later time? (Y/N)

Note: "Documentation" includes information on the wiki and .rst files in doc/source/,
which are used to create the online technical docs at https://readthedocs.org/projects/cice-consortium-cice/.

• Other Relevant Details:

[duvivier]

This all looks fine to me. :)

[eclare108213]

looks fine to me too