Support all of Unicode in modern js engines

Changes:

* syntax consistency and comments accuracy
* handling of all other escapes in, say, v8, via [`String.prototype.normalize('NFKD')`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/normalize), when feature detected and working

This gets us support for all quixotic things like `ṩ` => `s`, as `"ṩ".normalize('NFKD')` breaks the composed (no matter how it is encoded – `\u1E69`, `\u1E9B\u0323` and `\u017F\u0323\u0307` are all the same glyph, encoded with different Unicode composition styles) character into its most basic form, with various combining characters we strip. (It also breaks apart the ™ sign into the letters TM, and so on.)
Changed to match what was implemented.