Consistently use StableHLO mnemonics in the spec (#251)
Consistently use StableHLO mnemonics in the spec (#251)

* Rename "max" and "min" in the TOC to "maximum" and "minimum" to follow
the StableHLO mnemonics.
* Rename "exp" in the TOC and in the actual spec to follow the StableHLO
mnemonics.
  * Reorder `sqrt` and `subtract` to keep alphabetical order.
  * Also, remove the deprecated way of specifying op syntax.
openxla/stablehlo,openxla/stablehlo,openxla/stablehlo,openxla/stablehlo