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/io.rst

@@ -0,0 +1,212 @@
+====================
+IO Classes and Types
+====================
+
+Classes for managing Revolution Pi inputs and outputs.
+
+.. currentmodule:: revpimodio2.io
+
+IOList
+======
+
+.. autoclass:: IOList
+   :members:
+   :undoc-members:
+   :show-inheritance:
+   :special-members: __init__, __getitem__, __contains__, __iter__
+
+   Container for accessing all IO objects.
+
+   The IOList provides multiple ways to access IOs:
+
+   * **Direct attribute access**: ``rpi.io.button.value``
+   * **String-based access**: ``rpi.io["button"].value``
+   * **Iteration**: ``for io in rpi.io: ...``
+
+   **Example:**
+
+   .. code-block:: python
+
+       # Direct access
+       value = rpi.io.I_1.value
+       rpi.io.O_1.value = True
+
+       # String-based access
+       value = rpi.io["I_1"].value
+
+       # Check if IO exists
+       if "sensor" in rpi.io:
+           print(rpi.io.sensor.value)
+
+       # Iterate all IOs
+       for io in rpi.io:
+           print(f"{io.name}: {io.value}")
+
+IOBase
+======
+
+.. autoclass:: IOBase
+   :members:
+   :undoc-members:
+   :show-inheritance:
+   :special-members: __init__
+
+   Base class for all IO objects.
+
+   **Properties:**
+
+
+
+      IO name from piCtory configuration
+
+
+
+      Current IO value (read/write)
+
+
+
+      Byte address in process image
+
+
+
+      Byte length (0 for single bits)
+
+
+
+      IO type: 300=INPUT, 301=OUTPUT, 302=MEMORY
+
+
+
+      Whether value is signed
+
+
+
+      "little" or "big" endian
+
+
+
+      Configured default value from piCtory
+
+
+
+      Comment/description from piCtory
+
+
+
+      Export flag status
+
+Event Registration Methods
+---------------------------
+
+
+Value Manipulation Methods
+---------------------------
+
+
+IntIO
+=====
+
+.. autoclass:: IntIO
+   :members:
+   :undoc-members:
+   :show-inheritance:
+   :special-members: __init__
+
+   IO objects with integer value access.
+
+   **Example:**
+
+   .. code-block:: python
+
+       # Get integer value
+       temp = rpi.io.temperature.get_intvalue()
+
+       # Set integer value
+       rpi.io.setpoint.set_intvalue(1500)
+
+Integer Value Methods
+---------------------
+
+
+IntIOCounter
+============
+
+.. autoclass:: IntIOCounter
+   :members:
+   :undoc-members:
+   :show-inheritance:
+   :special-members: __init__
+
+   Counter input objects with reset capability.
+
+   **Example:**
+
+   .. code-block:: python
+
+       # Read counter
+       count = rpi.io.counter.value
+
+       # Reset counter
+       rpi.io.counter.reset()
+
+StructIO
+========
+
+.. autoclass:: StructIO
+   :members:
+   :undoc-members:
+   :show-inheritance:
+   :special-members: __init__
+
+   Structured IO with format strings for complex data types.
+
+   **Example:**
+
+   .. code-block:: python
+
+       # Get structured value
+       value = rpi.io.sensor_data.get_structvalue()
+
+Structured Value Methods
+------------------------
+
+
+MemIO
+=====
+
+.. autoclass:: MemIO
+   :members:
+   :undoc-members:
+   :show-inheritance:
+   :special-members: __init__
+
+   Memory IO with variant value access (string or integer).
+
+RelaisOutput
+============
+
+.. autoclass:: RelaisOutput
+   :members:
+   :undoc-members:
+   :show-inheritance:
+   :special-members: __init__
+
+   Relay output with switching cycle counter.
+
+   **Example:**
+
+   .. code-block:: python
+
+       # Get number of switching cycles
+       cycles = rpi.io.relay.get_switching_cycles()
+
+IOEvent
+=======
+
+.. autoclass:: IOEvent
+   :members:
+   :undoc-members:
+   :show-inheritance:
+   :special-members: __init__
+
+   Internal class for IO event management.