[esp] Add ESP-IDF cmake example.

esp/cpp/04_esp-idf-arduino/.gitignore

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+build
+managed_components
+dependencies.lock
+sdkconfig.old

esp/cpp/04_esp-idf-arduino/CMakeLists.txt

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+# For more information about build system see
+# https://docs.espressif.com/projects/esp-idf/en/latest/api-guides/build-system.html
+# The following five lines of boilerplate have to be in your project's
+# CMakeLists in this exact order for cmake to work correctly
+cmake_minimum_required(VERSION 3.26)
+
+include($ENV{IDF_PATH}/tools/cmake/project.cmake)
+
+project(
+    #[[NAME]]   esp-idf-arduino
+    VERSION     0.1
+    DESCRIPTION "Example ESP-IDF cmake project"
+    LANGUAGES   CXX
+)
+
+# For writing pure cmake components, see the documentation
+# https://docs.espressif.com/projects/esp-idf/en/stable/esp32/api-guides/build-system.html#writing-pure-cmake-components
+idf_build_set_property(COMPILE_OPTIONS "-Wno-error" APPEND)

esp/cpp/04_esp-idf-arduino/README.md

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+# 04_esp-idf-arduino
+
+There is no schematic for this example, it simply prints some output to the serial monitor at 115200.
+This is more of a build system example for untethering yourself from the Arduino IDE.
+
+To build this example you can run the following commands.
+
+```bash
+# See Dependencies section below for instructions.
+source ~/path/to/esp-idf/export.sh
+
+mkdir build
+cd build
+cmake ..
+make -j $(nproc)
+
+# Flash the example to the ESP.
+make flash
+
+# Check the serial monitor for 'Hello world!' output.
+idf.py monitor -b 115200
+```
+
+To flash to your ESP or access the `idf.py menuconfig` menu from the ESP-IDF you can run the same commands with `make`.
+
+```bash
+make flash
+make menuconfig
+```
+
+If Ninja is preferred:
+
+```bash
+mkdir build
+cd build
+cmake .. -G Nina
+ninja
+```
+
+## Dependencies
+
+Install the [ESP-IDF](https://github.com/espressif/esp-idf?tab=readme-ov-file#setup-build-environment)
+
+```bash
+# https://docs.espressif.com/projects/esp-idf/en/v5.3.2/esp32/get-started/linux-macos-setup.html#for-linux-users
+sudo apt-get install -y git wget flex bison gperf python3 python3-pip python3-venv cmake ninja-build ccache libffi-dev libssl-dev dfu-util libusb-1.0-0
+
+git clone -b v5.3.2 --recursive https://github.com/espressif/esp-idf
+cd esp-idf
+./install.sh
+. ./export.sh
+```
+
+In CLion there is an official [Serial Monitor](https://plugins.jetbrains.com/plugin/8031-serial-port-monitor) plugin, or use ESP-IDF -
+
+```bash
+idf.py monitor -b 115200
+```
+
+## Starting Over
+
+To set up this project from scratch the following commands were used
+
+```bash
+# My example project directory
+cd ~/Code/klips/esp/cpp/04_esp-idf-arduino
+idf.py set-target esp32
+idf.py add-dependency "espressif/arduino-esp32^3.1.1"
+
+# Autostart Arduino for use of `loop()` and `setup()` functions
+# You can also use the esp-idf `app_main()` function if preferred
+# https://docs.espressif.com/projects/arduino-esp32/en/latest/esp-idf_component.html#configuration
+# You can alternatively do this in the GUI tool `idf.py menuconfig`
+echo "CONFIG_AUTOSTART_ARDUINO=y" >> sdkconfig
+sed -i -e 's/CONFIG_FREERTOS_HZ=100/CONFIG_FREERTOS_HZ=1000/' sdkconfig
+
+# Build the project
+idf.py build
+```
+
+To set this project up in CLion, see [JetBrains documentation](https://www.jetbrains.com/help/clion/esp-idf.html#env-vars).

esp/cpp/04_esp-idf-arduino/main/CMakeLists.txt

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+idf_component_register(
+    SRCS "main.cpp"
+    INCLUDE_DIRS "."
+)

esp/cpp/04_esp-idf-arduino/main/idf_component.yml

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+## IDF Component Manager Manifest File
+dependencies:
+  ## Required IDF version
+  idf:
+    version: '>=4.1.0'
+  # # Put list of dependencies here
+  # # For components maintained by Espressif:
+  # component: "~1.0.0"
+  # # For 3rd party components:
+  # username/component: ">=1.0.0,<2.0.0"
+  # username2/component2:
+  #   version: "~1.0.0"
+  #   # For transient dependencies `public` flag can be set.
+  #   # `public` flag doesn't have an effect dependencies of the `main` component.
+  #   # All dependencies of `main` are public by default.
+  #   public: true
+  espressif/arduino-esp32: ^3.1.1

esp/cpp/04_esp-idf-arduino/main/main.cpp

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+#include "Arduino.h"
+
+void setup() {
+  Serial.begin(115200);
+}
+
+void loop() {
+  Serial.println("Hello world!");
+  delay(1000);
+}