Refactor to proper PlatformIO library structure

- Move source files to src/ and headers to include/ directories
- Remove Arduino IDE specific files (.travis.yml, keywords.txt, library.properties, CMakeLists.txt, travis/)
- Update library.json with export section pointing to include/
- Add platformio.ini for development and testing
- Update .gitignore with PlatformIO-specific entries
- Update LICENSE with fork attribution
- Update README.md with PlatformIO-focused installation instructions

Verified working with:
- ESP8266 examples (Basic, Advanced)
- ESP32 examples (Basic)

All builds successful ✅

library.json

@@ -1,29 +1,40 @@
 {
   "name": "WiFiManager",
   "version": "2.0.17",
-  "keywords": "wifi,wi-fi,esp,esp8266,esp32,espressif8266,espressif32,nodemcu,wemos,arduino",
+  "keywords": [
+    "wifi",
+    "wi-fi",
+    "esp",
+    "esp8266",
+    "esp32",
+    "espressif8266",
+    "espressif32",
+    "nodemcu",
+    "wemos",
+    "arduino"
+  ],
   "description": "WiFi Configuration manager with web configuration portal for ESP boards",
-  "authors":
-  [
+  "authors": [
     {
-        "name": "tzapu",
-        "url": "https://github.com/tzapu"
+      "name": "tzapu",
+      "url": "https://github.com/tzapu"
     },
     {
-        "name": "tablatronix",
-        "url": "https://github.com/tablatronix",
-        "maintainer": true
+      "name": "tablatronix",
+      "url": "https://github.com/tablatronix",
+      "maintainer": true
     }
   ],
-  "repository":
-  {
+  "repository": {
     "type": "git",
-    "url": "https://github.com/tzapu/WiFiManager.git"
+    "url": "https://github.com/alexhopeoconnor/WiFiManager.git"
   },
   "frameworks": "arduino",
-  "platforms": 
-  [
+  "platforms": [
     "espressif8266",
     "espressif32"
-  ]
+  ],
+  "export": {
+    "include": "include"
+  }
 }