Add documentation

[ctreffs]

Description

This PR introduces comprehensive documentation for the FirebladeMath library using Swift-DocC. It encompasses setting up the documentation generation infrastructure, adding a new GitHub Actions workflow for automated documentation building and deployment, and adding inline documentation comments to the public API.

Changes

• Infrastructure:
  • Added swift-docc-plugin dependency to Package.swift.
  • Updated Makefile with targets for generating, previewing, and checking documentation coverage and links (docs, docs-preview, docs-generate, docs-check-coverage, docs-check-links).
• CI/CD:
  • Added .github/workflows/docs.yml to automatically build and deploy documentation to GitHub Pages on push to main/master branches.
• Source Code:
  • Added detailed API documentation comments (triple slash ///) to public functions, structs, and extensions across the codebase, including:
    • Math functions (abs, sin, cos, etc.)
    • Matrix types and operations (Mat3x3, Mat4x4, etc.)
    • Quaternion types and operations
    • Vector extensions and utilities
    • Geometry types (Point, Rect, Size)

Motivation

To improve the usability and discoverability of the library's features for developers, ensuring that all public APIs are well-documented and accessible via a hosted documentation site.