v2.0.0: Flutter plugin rewrite

What's Changed

• v2.0.0: Flutter plugin rewrite accroding to new guideline by @shajedulislam in #2
• readme updated by @shajedulislam in #3
• improved documentation & updated .gitignore by @shajedulislam in #4

New Contributors

• @shajedulislam made their first contribution in #2

Full Changelog: v1.0.5...v2.0.0