docs: add comprehensive documentation structure and API reference

Created topic-based documentation:
- basics.rst: core concepts and fundamental usage
- cyclic_programming.rst: PLC-style programming with Cycletools
- event_programming.rst: event-driven patterns and callbacks
- advanced.rst: gateway IOs, replace_io_file, watchdog management
- installation.rst and quickstart.rst: getting started guides

Added complete API reference in docs/api/:
- All device classes including ModularBaseConnect_4_5 and GatewayMixin
- I/O, helper, and main class documentation

Enhanced Sphinx configuration with RTD theme and improved autodoc settings.
Removed auto-generated modules.rst and revpimodio2.rst.

docs/installation.rst

@@ -0,0 +1,85 @@
+============
+Installation
+============
+
+System Requirements
+===================
+
+* Python 3.7 or higher
+* Revolution Pi hardware (Core, Core3, Connect, Compact, Flat)
+* piCtory configuration tool
+
+Prerequisites
+=============
+
+User Permissions
+----------------
+
+On Bookworm images, users must belong to the ``picontrol`` group::
+
+    sudo usermod -a -G picontrol username
+
+Log out and log back in for the group change to take effect.
+
+Installing RevPiModIO
+=====================
+
+Using pip
+---------
+
+Install from PyPI::
+
+    pip install revpimodio2
+
+From Source
+-----------
+
+Clone the repository and install::
+
+    git clone https://github.com/naruxde/revpimodio2.git
+    cd revpimodio2
+    pip install .
+
+Verify Installation
+===================
+
+Test the installation::
+
+    python3 -c "import revpimodio2; print(revpimodio2.__version__)"
+
+Optional Components
+===================
+
+RevPiPyLoad
+-----------
+
+For advanced features like XML-RPC server and MQTT integration::
+
+    sudo apt-get update
+    sudo apt-get install revpipyload
+
+Configure XML-RPC Server
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Edit ``/etc/revpipyload/revpipyload.conf``::
+
+    [XMLRPC]
+    xmlrpc = 1
+
+Configure access permissions in ``/etc/revpipyload/aclxmlrpc.conf``, then restart::
+
+    sudo service revpipyload restart
+
+RevPi Commander
+---------------
+
+RevPi Commander provides a GUI for testing I/O without programming:
+
+1. Download from `revpimodio.org <https://revpimodio.org/quellen/revpicommander/>`_
+2. Configure connection via File → Connections with your RevPi's IP address (port: 55123)
+3. Use "PLC watch mode" to monitor sensors and control outputs
+
+Next Steps
+==========
+
+After installation, proceed to :doc:`quickstart` to write your first program.