Add documentation and licensing / copying

• Add original license, authors, etc. in docs/
• Add contributing guidelines, issue template, & pull request template
• Update README with links, samples, output instructions, etc.

Initial release

Initial release, using Gnome's Adwaita icons

• Removes any style attributes
• Minifies/optimizes all SVGs
• Removes symlinks
• Removes most pre-defined fill colors, allowing developers/designers
  to control this using CSS
• Removes all/most useless attributes, such as rendering instructions