Editorial: Consistently represent expressions that include exponents

[gibson042]

This PR addresses two inconsistencies:

• Some expressions of the form "x^y - z" are missing spaces around the operator.
• Some uses of 𝔽/ℤ/ℝ wrap the argument in <emu-eqn> when it includes exponentiation, while others do not. Uses inside of <emu-alg> never include the wrapping, while uses outside of it are evenly split (but never wrap any argument without exponentiation, even if it uses other operations such as division with /):

  $ grep -v '^ *1[.]' spec.html | grep -o '[𝔽ℤℝ][(][^()]*\([(][^()]*[)][^()]*\)*[)]' | grep '<sup>' | sort | uniq -c
        1 𝔽(2<sup>32</sup> - 1)
        1 𝔽(-(2<sup>53</sup> - 1))
        2 𝔽(2<sup>53</sup> - 1)
        1 ℤ(-2<sup>63</sup>)
        1 ℤ(2<sup>63</sup> - 1)
        1 ℤ(2<sup>64</sup> - 1)
        1 𝔽(<emu-eqn>2<sup>15</sup> - 1</emu-eqn>)
        1 𝔽(<emu-eqn>-2<sup>15</sup></emu-eqn>)
        1 𝔽(<emu-eqn>2<sup>16</sup> - 1</emu-eqn>)
        1 𝔽(<emu-eqn>2<sup>31</sup> - 1</emu-eqn>)
        1 𝔽(<emu-eqn>-2<sup>31</sup></emu-eqn>)
        2 𝔽(<emu-eqn>2<sup>32</sup> - 1</emu-eqn>)

  Given the apparent lack of problems from the simpler form and the likelihood of forgetting the more complex form in the absence of lint warnings, I've opted for exclusive use of the former.