docs: rewrite README, add API.md, gitignore PROJECT_PLAN.md (#2)

- README: hero section, comparison table, quick start, features,
  usage examples, charset table, phased roadmap, contributing, about
- API.md: full reference for all exports with types and examples
- .gitignore: exclude PROJECT_PLAN.md (internal strategy doc)

Co-authored-by: Vaibhav Rajput <vaibhav@Vaibhavs-MacBook-Pro.local>

Author: vaibhav1312

.gitignore

@@ -4,3 +4,4 @@ dist/
 .DS_Store
 coverage/
 .env
+PROJECT_PLAN.md