[latexrefman] Adjust font size section

[Hefferon, Jim S.]

I added a paragraph on the warning that you get if you use \small, etc., inside math.  

I also reverted the \textrm{d} x for the integral.  I am aware that a standards org said to use that, but I think the other is common practice also and I am following Knuth's practice, p 168.

Jim

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"You’ve got to see the floor before you build the ceiling."  -- D Knuth