docs(readme): revise for 2.0 — tone, headings, tables, code samples

Behavior of the docs is unchanged; this is presentation work.

- Tone: drop "allows you to easily ...", "Boolean value indicating
  whether ..." and similar marketing/hedge phrasing throughout. Use
  direct verbs ("Fires when ...", "Suppresses ..."). Trim the API
  intro to one sentence.
- Headings normalized to sentence case and hyphens fixed: "Event
  function settings" -> "Event callbacks", "Local only settings" ->
  "Local-only settings", "Ajax only settings" -> "Ajax-only settings",
  "Non standard query/results" -> "Non-standard request / response
  format", "Default Options" -> "Default options", and similar.
- Tables:
    * Event callbacks now uses Callback / Signature / Description
      (was a two-column "Event setting / Function description").
    * Instance methods promoted from bullet list to two-column table.
    * General settings reordered into rough behavioral groups (input
      behavior, labels, grouping, callbacks, layout, container) instead
      of arbitrary order.
    * Defaults consistently quoted: `"auto"`, `"bottom"`, `"No results"`
      instead of mixing bare and backticked forms.
- Code samples:
    * var -> const in JS examples.
    * Template literals replace + concatenation.
    * console.log replaces alert (alert is poor sample practice now).
    * Custom-lookup example inlines done({...}) instead of using an
      intermediate variable.
    * transformResult sample uses Array.prototype.map instead of $.map.
    * Trailing commas + self-closing tag spacing match project Prettier
      config.
- Styling section: fold the `cursor: pointer` mobile-Safari note (was
  buried in Known Issues) into the minimal CSS block where consumers
  will actually see it. Issue #542 still cited.
- Known Issues now has one entry (the jQuery UI conflict) instead of
  two.
- Authors: Twitter handle link now points at x.com.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: tkirda-bison