doc: reorganize files

Separate various autogen files from the documentation .dox files.
Rename .dox files to match the intended tree structure.

doc/dox/overview.dox

@@ -0,0 +1,42 @@
+/** \page page_overview Overview
+
+PipeWire is a new low-level multimedia framework designed from scratch that
+aims to provide:
+
+- Graph based processing.
+- Support for out-of-process processing graphs with minimal overhead.
+- Flexible and extensible media format negotiation and buffer allocation.
+- Hard real-time capable plugins.
+- Achieve very low-latency for both audio and video processing.
+
+The framework is used to build a modular daemon that can be configured to:
+
+- Be a low-latency audio server with features like PulseAudio and/or JACK.
+- A video capture server that can manage hardware video capture devices and
+  provide access to them.
+- A central hub where video can be made available for other applications
+  such as the gnome-shell screencast API.
+
+
+# Motivation
+
+Linux has no unified framework for exchanging multimedia content between
+applications or even devices. In most cases, developers realized that
+a user-space daemon is needed to make this possible:
+
+- For video content, we typically rely on the compositor to render our
+  data.
+- For video capture, we usually go directly to the hardware devices, with
+  all security implications and inflexible routing that this brings.
+- For consumer audio, we use PulseAudio to manage and mix multiple streams
+  from clients.
+- For Pro audio, we use JACK to manage the graph of nodes.
+
+None of these solutions (except perhaps to some extent Wayland) however 
+were designed to support the security features that are required when
+dealing with flatpaks or other containerized applications. PipeWire
+aims to solve this problem and provides a unified framework to run both
+consumer and pro audio as well as video capture and processing in a
+secure way.
+
+*/