fix: harden close button rendering and refresh docs/examples

[dusan-maintains]

Summary

• render closeText as plain text instead of HTML when creating the close button
• improve ESC close handling by supporting event.key === 'Escape' and guarding null current modal
• refresh docs/examples CDN snippets and align README option docs with actual defaults

Why

• reduces injection risk through closeText
• improves keyboard-close reliability in modern browsers
• removes stale documentation/examples mismatch

Changes

• jquery.modal.js
• README.md
• examples/index.html

Test Plan

• open/close modal via close button, ESC, and overlay click
• set custom closeText containing HTML-like content and verify it renders as text
• verify docs/examples snippets match current defaults/versions

Compatibility

• no API changes
• no option/default behavior changes

[dusan-maintains]

Maintainer note: I kept this PR intentionally small and backward-compatible. If you prefer, I can split docs/example updates from runtime changes to simplify review.