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/api/index.rst

@@ -0,0 +1,148 @@
+.. _api_reference:
+
+=============
+API Reference
+=============
+
+Complete API reference for RevPiModIO2 Python library.
+
+.. contents:: Table of Contents
+   :local:
+   :depth: 2
+
+Overview
+========
+
+RevPiModIO provides several main classes for programming Revolution Pi hardware:
+
+* :class:`~revpimodio2.modio.RevPiModIO` - Main class for managing all devices and IOs
+* :class:`~revpimodio2.modio.RevPiModIOSelected` - Manage specific devices only
+* :class:`~revpimodio2.modio.RevPiModIODriver` - Write data to virtual device inputs
+* :class:`~revpimodio2.io.IOList` - Container for accessing IOs
+* :class:`~revpimodio2.io.IOBase` - Base class for all IO objects
+* :class:`~revpimodio2.helper.Cycletools` - Toolkit for cyclic programming
+* :class:`~revpimodio2.helper.EventCallback` - Event handler class
+
+Quick Examples
+==============
+
+Basic Usage
+-----------
+
+.. code-block:: python
+
+    import revpimodio2
+
+    # Initialize
+    rpi = revpimodio2.RevPiModIO(autorefresh=True)
+
+    # Read input and control output
+    if rpi.io.button.value:
+        rpi.io.led.value = True
+
+    # Cleanup
+    rpi.exit()
+
+Cyclic Programming
+------------------
+
+.. code-block:: python
+
+    import revpimodio2
+
+    rpi = revpimodio2.RevPiModIO(autorefresh=True)
+
+    def main_cycle(ct: revpimodio2.Cycletools):
+        if ct.first:
+            ct.var.counter = 0
+
+        if ct.changed(ct.io.sensor):
+            ct.var.counter += 1
+
+    rpi.cycleloop(main_cycle)
+
+Event-Driven Programming
+------------------------
+
+.. code-block:: python
+
+    import revpimodio2
+
+    rpi = revpimodio2.RevPiModIO(autorefresh=True)
+
+    def on_change(ioname, iovalue):
+        print(f"{ioname} = {iovalue}")
+
+    rpi.io.button.reg_event(on_change)
+    rpi.handlesignalend()
+    rpi.mainloop()
+
+Constants
+=========
+
+Edge Detection
+--------------
+
+.. py:data:: revpimodio2.RISING
+   :type: int
+
+   Detect low-to-high transitions
+
+.. py:data:: revpimodio2.FALLING
+   :type: int
+
+   Detect high-to-low transitions
+
+.. py:data:: revpimodio2.BOTH
+   :type: int
+
+   Detect any transition
+
+LED Colors
+----------
+
+.. py:data:: revpimodio2.OFF
+   :type: int
+
+   LED off
+
+.. py:data:: revpimodio2.GREEN
+   :type: int
+
+   Green LED
+
+.. py:data:: revpimodio2.RED
+   :type: int
+
+   Red LED
+
+IO Types
+--------
+
+.. py:data:: INP
+   :type: int
+   :value: 300
+
+   Input type
+
+.. py:data:: OUT
+   :type: int
+   :value: 301
+
+   Output type
+
+.. py:data:: MEM
+   :type: int
+   :value: 302
+
+   Memory type
+
+See Also
+========
+
+* :doc:`../installation` - Installation guide
+* :doc:`../quickstart` - Quick start guide
+* :doc:`../basics` - Core concepts
+* :doc:`../cyclic_programming` - Cyclic programming patterns
+* :doc:`../event_programming` - Event-driven programming patterns
+* :doc:`../advanced` - Advanced topics