Added function to export JSON and extract Metadata

[erseco]

This PR adds two key features to the ElpParser library:

• Export to JSON:
  The new exportJson() method allows saving parsed ELP data as a JSON file. It supports optional file paths and handles errors on encoding or write failure.

• Metadata Tree Retrieval:
  The new getMetadata() method returns a detailed metadata tree including Dublin Core, LOM, LOM-ES, and page structure.

Docs

• README.md and docs/index.md now include usage examples and updated feature lists.
• docs/api.md includes details on the new methods.

Tests

• Added test fixtures for metadata and JSON export (04_La_Ilustracion.*).
• New unit tests cover exportJson() and getMetadata().

Utilities

• Introduced remove_accents and seems_utf8 helper functions for better metadata handling.

[Copilot]

Pull Request Overview

This PR introduces two new features for the ElpParser library: exporting parsed data to JSON and retrieving a detailed metadata tree.

• Adds the exportJson() method to output JSON data (either as a string or directly to a file)
• Introduces the getMetadata() method to provide a rich metadata structure including Package, Dublin Core, LOM, and LOM-ES information
• Updates tests and documentation (README.md, docs/index.md, docs/api.md) to cover and explain the new features

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/Unit/ElpParserTest.php	Added unit tests verifying the functionality of exportJson() and getMetadata()
tests/Fixtures/04_La_Ilustracion.json	New fixture for exported JSON data; includes a placeholder for cloze_text in a ClozeIdevice entry
tests/Fixtures/04_La_Ilustracion.expected.json	Added expected JSON structure for testing exportJson()
src/ElpParser.php	New methods exportJson() and getMetadata() added along with associated helper functions
docs/index.md, docs/api.md, README.md	Updated documents to include usage examples and API details for the new methods

[Copilot]

A comment is present inside the JSON array for 'cloze_text', which is not valid JSON syntax. Either remove the comment or replace it with valid JSON content (for example, an empty array) to ensure the fixture file is parseable.

Suggested change

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