Consolidate Block modules into a single file, block.ex

[bradhanks]

Refactors the block-related modules by consolidating them into a single file (block.ex) and introduces type definitions for EarmarkParser.Block.t and EarmarkParser.Link.t. The goal is to improve code organization, maintainability, and type safety.

Related Issue: #166

Changes:

1. Removed the block folder and all associated module files.

2. Created lib/earmark_parser/block.ex to house the consolidated module.

3. Consolidated all child modules into a single file.

4. Added type definition for EarmarkParser.Block.t.

5. Added type definition for EarmarkParser.Link.t.

Benefits:

• Improved code organization and maintainability.
• Enhanced type safety and clarity through type definitions (want to be able to add specification with Block.t which wasn't currently possible)
• Simplified file structure for easier navigation and future development.

[bradhanks]

mix test worked for me:

50 doctests, 1005 tests, 0 failures, 5 excluded, 1 skipped