Align editing style with common "standards"

Two editing "quirks" the course material harder to read:*

- Idiosyncratic placement of footnote references before a punctuation mark (example: "$33,460,000,000,000,000,000,000,000^{2,3}$start superscript, 2, comma, 3, end superscript." in https://www.khanacademy.org/science/biology/water-acids-and-bases/acids-bases-and-ph/a/acids-bases-ph-and-bufffers; should read: "33,460,000,000,000,000,000,000,000.$^{2,3}$start superscript, 2, comma, 3, end superscript"). See, for instance, the Chicago Manual of Style.

- In equations, variables are written in italics, while names and abbreviations should be written in roman (example: in https://www.khanacademy.org/science/physics/thermodynamics/temp-kinetic-theory-ideal-gas-law/a/what-is-the-maxwell-boltzmann-distribution you introduce the concept of the average speed and denote it as $v_{avg}$; however, "avg" is not a variable, but an abbreviations for "average"; the denotation should thus read $v_\textrm{avg}$. See ISO/IEC 80000-1 for more details.

*I am using pseudo-Latex syntax for mathematical text for clarity