Try to build against PIO (#598)

travis/build-pio.sh

@@ -0,0 +1,24 @@
+#!/bin/bash
+
+BOARD=$1
+
+echo -e "travis_fold:start:install_pio"
+pip install -U platformio
+
+platformio lib install https://github.com/bblanchon/ArduinoJson.git
+
+case $BOARD in
+esp32dev)
+  platformio lib -g install https://github.com/me-no-dev/AsyncTCP.git
+  ;;
+esp12e)
+  platformio lib -g install https://github.com/me-no-dev/ESPAsyncTCP.git || true
+  ;;
+esac
+echo -e "travis_fold:end:install_pio"
+
+echo -e "travis_fold:start:test_pio"
+for EXAMPLE in $PWD/examples/*/*.ino; do
+    platformio ci $EXAMPLE -l '.' -b $BOARD
+done
+echo -e "travis_fold:end:test_pio"