[latexrefman] Add section for \mathstrut

[Hefferon, Jim S.]

Added a section for \mathstrut.  The section for \vphantom used Knuth's sqrt{} example that is better with \mathstrut, so I made a new example better done with \vphantom.

Jim

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[r]ecently I heard (not without a complacent simper) that the best bookshop in America had moved my books across the aisle from Fiction to Literature.  --Patrick O'Brian, 1995