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-sample-plugin/README.md

@@ -0,0 +1,96 @@
+# MarkItDown Sample Plugin
+
+[![PyPI](https://img.shields.io/pypi/v/markitdown.svg)](https://pypi.org/project/markitdown/)
+![PyPI - Downloads](https://img.shields.io/pypi/dd/markitdown)
+[![Built by AutoGen Team](https://img.shields.io/badge/Built%20by-AutoGen%20Team-blue)](https://github.com/microsoft/autogen)
+
+
+This project shows how to create a sample plugin for MarkItDown. The most important parts are as follows:
+
+FNext, implement your custom DocumentConverter:
+
+```python
+from typing import Union
+from markitdown import DocumentConverter, DocumentConverterResult
+
+class RtfConverter(DocumentConverter):
+    def convert(self, local_path, **kwargs) -> Union[None, DocumentConverterResult]:
+        # Bail if not an RTF file 
+        extension = kwargs.get("file_extension", "")
+        if extension.lower() != ".rtf":
+            return None
+
+	# Implement the conversion logic here ...
+
+        # Return the result
+        return DocumentConverterResult(
+            title=title,
+            text_content=text_content,
+        )
+```
+
+Next, make sure your package implements and exports the following:
+
+```python
+# The version of the plugin interface that this plugin uses. 
+# The only supported version is 1 for now.
+__plugin_interface_version__ = 1 
+
+# The main entrypoint for the plugin. This is called each time MarkItDown instances are created.
+def register_converters(markitdown: MarkItDown, **kwargs):
+    """
+    Called during construction of MarkItDown instances to register converters provided by plugins.
+    """
+
+    # Simply create and attach an RtfConverter instance
+    markitdown.register_converter(RtfConverter())
+```
+
+
+Finally, create an entrypoint in the `pyproject.toml` file:
+
+```toml
+[project.entry-points."markitdown.plugin"]
+sample_plugin = "markitdown_sample_plugin"
+```
+
+Here, the value of `sample_plugin` can be any key, but should ideally be the name of the plugin. The value is the fully qualified name of the package implementing the plugin.
+
+
+## Installation
+
+To use the plugin with MarkItDown, it must be installed. To install the plugin from the current directory use:
+
+```bash
+pip install -e .
+```
+
+Once the plugin package is installed, verify that it is available to MarkItDown by running:
+
+```bash
+markitdown --list-plugins
+```
+
+To use the plugin for a conversion use the `--use-plugins` flag. For example, to convert a PDF:
+
+```bash
+markitdown --use-plugins path-to-file.pdf
+```
+
+In Python, plugins can be enabled as follows:
+
+```python
+from markitdown import MarkItDown
+
+md = MarkItDown(enable_plugins=True) 
+result = md.convert("path-to-file.pdf")
+print(result.text_content)
+```
+
+## 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.