Update converter API, user streams rather than file paths (#1088)

* Updated DocumentConverter interface
* Updated all DocumentConverter classes
* Added support for various new audio files.
* Updated sample plugin to new DocumentConverter interface.
* Updated project README with notes about changes, and use-cases.
* Updated DocumentConverter documentation.
* Move priority to outside DocumentConverter, allowing them to be reprioritized, and keeping the DocumentConverter interface simple.

---------

Co-authored-by: Kenny Zhang <kzhang678@gmail.com>

README.md

@@ -7,9 +7,11 @@
 > [!IMPORTANT]
 > Breaking changes between 0.0.1 to 0.0.2:
 > * Dependencies are now organized into optional feature-groups (further details below). Use `pip install markitdown[all]` to have backward-compatible behavior. 
+> * The DocumentConverter class interface has changed to read from file-like streams rather than file paths. *No temporary files are created anymore*. If you are the maintainer of a plugin, or custom DocumentConverter, you likely need to update your code. Otherwise, if only using the MarkItDown class or CLI (as in these examples), you should not need to change anything.
 
-MarkItDown is a utility for converting various files to Markdown (e.g., for indexing, text analysis, etc).
-It supports:
+MarkItDown is a lightweight Python utility for converting various files to Markdown for use with LLMs and related text analysis pipelines. To this end, it is most comparable to [textract](https://github.com/deanmalmgren/textract), but with a focus on preserving important document structure and content as Markdown (including: headings, lists, tables, links, etc.) While the output is often reasonably presentable and human-friendly, it is meant to be consumed by text analysis tools -- and may not be the best option for high-fidelity document conversions for human consumption.
+
+At present, MarkItDown supports:
 
 - PDF
 - PowerPoint
@@ -23,6 +25,17 @@ It supports:
 - Youtube URLs
 - ... and more!
 
+## Why Markdown?
+
+Markdown is extremely close to plain text, with minimal markup or formatting, but still
+provides a way to represent important document structure. Mainstream LLMs, such as
+OpenAI's GPT-4o, natively "_speak_" Markdown, and often incorporate Markdown into their
+responses unprompted. This suggests that they have been trained on vast amounts of
+Markdown-formatted text, and understand it well. As a side benefit, Markdown conventions
+are also highly token-efficient.
+
+## Installation
+
 To install MarkItDown, use pip: `pip install markitdown[all]`. Alternatively, you can install it from the source:
 
 ```bash