Cleanup and refactor, in preparation for plugin support. (#318)

* Work started moving converters to individual files.
* Significant cleanup and refactor.
* Moved everything to a packages subfolder.
* Added sample plugin.
* Added instructions to the README.md
* Bumped version, and added a note about compatibility.

packages/markitdown/README.md

@@ -0,0 +1,52 @@
+# MarkItDown
+
+> [!IMPORTANT]
+> MarkItDown is a Python package and command-line utility for converting various files to Markdown (e.g., for indexing, text analysis, etc). 
+>
+> For more information, and full documentation, see the project [README.md](https://github.com/microsoft/markitdown) on GitHub.
+
+## Installation
+
+From PyPI:
+
+```bash
+pip install markitdown
+```
+
+From source:
+
+```bash
+git clone git@github.com:microsoft/markitdown.git
+cd markitdown
+pip install -e packages/markitdown
+```
+
+## Usage
+
+### Command-Line
+
+```bash
+markitdown path-to-file.pdf > document.md
+```
+
+### Python API
+
+```python
+from markitdown import MarkItDown
+
+md = MarkItDown()
+result = md.convert("test.xlsx")
+print(result.text_content)
+```
+
+### More Information
+
+For more information, and full documentation, see the project [README.md](https://github.com/microsoft/markitdown) on GitHub.
+
+## Trademarks
+
+This project may contain trademarks or logos for projects, products, or services. Authorized use of Microsoft
+trademarks or logos is subject to and must follow
+[Microsoft's Trademark & Brand Guidelines](https://www.microsoft.com/en-us/legal/intellectualproperty/trademarks/usage/general).
+Use of Microsoft trademarks or logos in modified versions of this project must not cause confusion or imply Microsoft sponsorship.
+Any use of third-party trademarks or logos are subject to those third-party's policies.