v5.1.1

• 064383a fix: do not use fs-extra in cli
• 585f3b3 chore: remove no longer needed node-fetch
• 07b55af feat(#72): provide command line interface
• af96727 fix: throw error if URL is provided but fetch is not available
• 8bca3b7 fix: Blob might be undefined
• 2192931 test: add tests for valid input formats
• ac75816 docs: add contributors to copyright
• 5623a60 feat: adopt typescript declarations to new implementation
• bcef7f4 refactor: use helper function to parse pages string
• 6d3636c refactor: use common PDFMergerBase class for common functionality