Implement the sensor-sample for PlatformIO

closes mcci-catena#218

examples/esp32_platformio/.gitignore

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+.pio
+.vscode/.browse.c_cpp.db*
+.vscode/c_cpp_properties.json
+.vscode/launch.json
+.vscode/ipch
+include/secrets.h
+

examples/esp32_platformio/esp32_platformio.code-workspace

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+{
+	"folders": [
+		{
+			"path": "."
+		}
+	],
+	"settings": {}
+}

examples/esp32_platformio/include/secrets.h.template

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+#define SECRETS
+
+// deveui, little-endian
+static const std::uint8_t deveui[] = { 0xAA, 0xBB, 0xCC, 0x00, 0x00, 0xDD, 0xEE, 0xFF };
+
+// appeui, little-endian
+static const std::uint8_t appeui[] = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };
+
+// appkey: just a string of bytes, sometimes referred to as "big endian".
+static const std::uint8_t appkey[] = { 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88, 0x99, 0xAA, 0xBB, 0xCC, 0xDD, 0xEE, 0xFF, 0x00 };

examples/esp32_platformio/lib/README

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+
+This directory is intended for project specific (private) libraries.
+PlatformIO will compile them to static libraries and link into executable file.
+
+The source code of each library should be placed in a an own separate directory
+("lib/your_library_name/[here are source files]").
+
+For example, see a structure of the following two libraries `Foo` and `Bar`:
+
+|--lib
+|  |
+|  |--Bar
+|  |  |--docs
+|  |  |--examples
+|  |  |--src
+|  |     |- Bar.c
+|  |     |- Bar.h
+|  |  |- library.json (optional, custom build options, etc) https://docs.platformio.org/page/librarymanager/config.html
+|  |
+|  |--Foo
+|  |  |- Foo.c
+|  |  |- Foo.h
+|  |
+|  |- README --> THIS FILE
+|
+|- platformio.ini
+|--src
+   |- main.c
+
+and a contents of `src/main.c`:
+```
+#include <Foo.h>
+#include <Bar.h>
+
+int main (void)
+{
+  ...
+}
+
+```
+
+PlatformIO Library Dependency Finder will find automatically dependent
+libraries scanning project source files.
+
+More information about PlatformIO Library Dependency Finder
+- https://docs.platformio.org/page/librarymanager/ldf.html

examples/esp32_platformio/platformio.ini

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+; PlatformIO Project Configuration File
+;
+;   Build options: build flags, source filter
+;   Upload options: custom upload port, speed and extra flags
+;   Library options: dependencies, extra library storages
+;   Advanced options: extra scripting
+;
+; Please visit documentation for the other options and examples
+; https://docs.platformio.org/page/projectconf.html
+
+[env:ttgo-lora32-v21]
+platform = espressif32
+board = ttgo-lora32-v21
+framework = arduino
+lib_deps = 
+	https://github.com/mcci-catena/arduino-lorawan
+;	Ofiicial Release is missing a Patch that causes a Boot-Loop #204
+;	mcci-catena/MCCI Arduino LoRaWAN Library @ ^0.9.2
+	thesolarnomad/LoRa Serialization@^3.2.1
+
+monitor_speed = 115200
+
+build_flags =
+;	Define Frequancy
+	-DCFG_eu868
+;	mitigate "multiple definitions hal_init" - Bug
+	-D hal_init=LMICHAL_init
+	-DLMIC_DEBUG_LEVEL=1
+	-D_DEBUG_MODE_