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/helper.rst

@@ -0,0 +1,194 @@
+==============
+Helper Classes
+==============
+
+Helper classes for cyclic and event-driven programming.
+
+.. currentmodule:: revpimodio2.helper
+
+Cycletools
+==========
+
+.. autoclass:: Cycletools
+   :members:
+   :undoc-members:
+   :show-inheritance:
+   :special-members: __init__
+
+   Toolkit provided to cyclic functions via ``.cycleloop()``.
+
+   This class provides tools for cyclic functions including timing flags
+   and edge markers. Note that edge markers (flank flags) are all True
+   during the first cycle!
+
+   **Attributes:**
+
+
+
+      Reference to RevPiModIO core object
+
+
+
+      Reference to RevPiModIO device object
+
+
+
+      Reference to RevPiModIO io object
+
+
+
+      True only on first cycle
+
+
+
+      True when shutdown signal received
+
+
+
+      Current function execution time in seconds
+
+
+
+      Container for cycle-persistent variables
+
+   **Toggle Flags** - Alternate between True/False:
+
+
+
+      1 cycle True, 1 cycle False
+
+
+
+      2 cycles True, 2 cycles False
+
+
+
+      5 cycles True, 5 cycles False
+
+
+
+      10 cycles True, 10 cycles False
+
+
+
+      20 cycles True, 20 cycles False
+
+   **Flank Flags** - True every nth cycle:
+
+
+
+      True every 5 cycles
+
+
+
+      True every 10 cycles
+
+
+
+      True every 15 cycles
+
+
+
+      True every 20 cycles
+
+   **Example:**
+
+   .. code-block:: python
+
+       def main(ct: revpimodio2.Cycletools):
+           if ct.first:
+               # Initialize
+               ct.var.counter = 0
+
+           # Main logic
+           if ct.changed(ct.io.sensor):
+               ct.var.counter += 1
+
+           # Blink LED using timing flag
+           ct.io.led.value = ct.flag5c
+
+           if ct.last:
+               # Cleanup
+               print(f"Final: {ct.var.counter}")
+
+Change Detection
+----------------
+
+
+Timer Functions
+---------------
+
+On-Delay Timers
+~~~~~~~~~~~~~~~
+
+
+Off-Delay Timers
+~~~~~~~~~~~~~~~~
+
+
+Pulse Timers
+~~~~~~~~~~~~
+
+
+EventCallback
+=============
+
+.. autoclass:: EventCallback
+   :members:
+   :undoc-members:
+   :show-inheritance:
+   :special-members: __init__
+
+   Thread for internal event function calls.
+
+   This class is passed to threaded event handlers registered with
+   ``as_thread=True``. The event function receives this thread object
+   as a parameter to access event information and control execution.
+
+   **Attributes:**
+
+
+
+      Name of IO that triggered the event
+
+
+
+      Value of IO when event was triggered
+
+
+
+      Threading event for abort conditions
+
+   **Example:**
+
+   .. code-block:: python
+
+       def threaded_handler(eventcallback: revpimodio2.EventCallback):
+           print(f"{eventcallback.ioname} = {eventcallback.iovalue}")
+
+           # Interruptible wait (3 seconds)
+           if eventcallback.exit.wait(3):
+               print("Wait interrupted!")
+               return
+
+           # Check if stop was called
+           if eventcallback.exit.is_set():
+               return
+
+       # Register as threaded event
+       rpi.io.button.reg_event(threaded_handler, as_thread=True)
+
+Methods
+-------
+
+
+ProcimgWriter
+=============
+
+.. autoclass:: ProcimgWriter
+   :members:
+   :undoc-members:
+   :show-inheritance:
+   :special-members: __init__
+
+   Internal thread for process image writing and event management.