Add initial project structure and core functionality for ArchDoc

- Created `.gitignore` files for various directories to exclude unnecessary files.
- Added `PLAN.md` to outline the project goals and architecture documentation generation.
- Implemented the `archdoc-cli` with a command-line interface for initializing and generating documentation.
- Developed the `archdoc-core` library for analyzing Python projects and generating architecture documentation.
- Included caching mechanisms to optimize repeated analysis.
- Established a comprehensive test suite to ensure functionality and error handling.
- Updated `README.md` to provide an overview and installation instructions for ArchDoc.

archdoc-core/tests/golden/files/example_architecture.md

@@ -0,0 +1,60 @@
+# Architecture Documentation
+
+Generated at: 1970-01-01 00:00:00 UTC
+
+## Overview
+
+This document provides an overview of the architecture for the project.
+
+## Modules
+
+### example.py
+
+File: `example.py`
+
+#### Imports
+
+- `os`
+- `typing.List`
+
+#### Symbols
+
+##### Calculator
+
+- Type: Class
+- Signature: `class Calculator`
+- Purpose: extracted from AST
+
+##### Calculator.__init__
+
+- Type: Function
+- Signature: `def __init__(...)`
+- Purpose: extracted from AST
+
+##### Calculator.add
+
+- Type: Function
+- Signature: `def add(...)`
+- Purpose: extracted from AST
+
+##### Calculator.multiply
+
+- Type: Function
+- Signature: `def multiply(...)`
+- Purpose: extracted from AST
+
+##### process_numbers
+
+- Type: Function
+- Signature: `def process_numbers(...)`
+- Purpose: extracted from AST
+
+## Metrics
+
+### Critical Components
+
+No critical components identified.
+
+### Component Dependencies
+
+Dependency analysis not yet implemented.