Formatting Improvements, Preload Polyfill Update

• Add fallback for cases when no assets are registered.
• Clean up plugin code structure.
• Switch from yarn to npm for JS package management.
• Update preload polyfill for CSS preloading.
• More intelligently load preload polyfill.

Preload and Preconnect Bug Fixes, Typo Fixes

• Fix bug causing duplicate preload links being generated for some assets.
• Fix bug causing preconnect links to have incorrectly formatted href values.
• Fix typos in documentation.

Minor UI Bug Fixes / Improvements

Address minor UI issues, as well as a small typo.

Introduce Support for Preconnect Hints, Improve Docs & UI

v1.1.0

Add support for preconnect hints, improve documentation and UI.