Enhance documentation and testing for ExampleEngine in Fess script plugin

[marevol]

This update significantly improves the fess-script-example plugin by enhancing its documentation and test coverage:

• README.md: Rewritten and expanded with detailed descriptions, usage instructions, development guide, project structure, and contribution guidelines.
• ExampleEngine.java: Added comprehensive JavaDoc comments to improve code readability and maintainability.
• ExampleEngineTest.java: Extended with 19 additional test cases, covering:
• Null and empty inputs
• Special characters and multilingual content
• Template integrity and return type validation
• Multiple engine instances and parameter map variations

These changes aim to serve both as a functional example and a learning resource for developers creating custom Fess script engines.

[Copilot]

Pull Request Overview

This PR enhances the fess-script-example plugin with comprehensive documentation improvements and extensive test coverage expansion. The changes transform the plugin from a basic example into a well-documented learning resource for developers creating custom Fess script engines.

• Comprehensive README.md rewrite with detailed usage instructions, development guide, and project structure
• Added JavaDoc documentation to ExampleEngine.java for better code readability
• Expanded test suite with 19 additional test cases covering edge cases, multilingual content, and validation scenarios

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
README.md	Complete rewrite with comprehensive documentation, installation guide, usage examples, and development instructions
ExampleEngine.java	Added detailed JavaDoc comments for class and methods, plus explicit constructor
ExampleEngineTest.java	Added 19 comprehensive test cases covering null/empty inputs, special characters, multilingual content, and edge cases

Comments suppressed due to low confidence (1)

src/test/java/org/codelibs/fess/script/example/ExampleEngineTest.java:134

• The assertSame check assumes string interning behavior, but since getName() returns a string literal, this test may be implementation-dependent. Consider using assertEquals instead to test functional equality rather than object identity.

        assertSame(name1, name2);

[Copilot]

[nitpick] The explicit constructor with super() call is redundant since Java provides a default no-argument constructor that calls super() automatically. Consider removing this constructor unless it serves a specific documentation purpose.

Suggested change

	/**
	* Creates a new instance of ExampleEngine.
	*/
	public ExampleEngine() {
	super();
	}
	/**
	// Removed redundant constructor and its associated comment.
	/**