Enhance README with theme support and update license information

- Added multiple built-in themes and custom CSS support to the README.
- Updated the license section to specify GNU General Public License v3.0 (GPL-3.0-or-later).

Refactor Tailwind CSS for improved utility classes

- Introduced new utility classes for spacing, margins, and borders in tailwind.css.
- Added support for additional colors and background utilities.
- Enhanced gradient and shadow utilities for better customization.

Refactor lyrics sharing functionality in lyrics_panel.rs

- Removed the build_screenshot_share_caption function to simplify sharing logic.
- Updated share_screenshot_lyrics_image to eliminate unused share_text parameter.
- Improved logic to check for shareable lyric lines before sharing.

Author: AD-Archer

Cargo.toml

@@ -3,6 +3,7 @@ name = "rustysound"
 version = "3.0.0"
 authors = ["ad-archer <antonioarcher.dev@gmail.com>"]
 edition = "2021"
+license = "GPL-3.0-or-later"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html