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/integration_tests.rs

@@ -0,0 +1,13 @@
+//! Integration tests for ArchDoc
+
+// Include golden tests
+mod golden;
+mod error_handling;
+mod caching;
+mod integration_detection;
+mod enhanced_analysis;
+
+// Run all tests
+fn main() {
+    // This is just a placeholder - tests are run by cargo test
+}