minor changes needed to build with platformio

I prefer platformio over the arduino IDE because
it automatically does library dependencies and
has lots of other goodness.

To build and install to a connected device just do:

pio run

.gitignore

@@ -1,3 +1,3 @@
-
+.pio
 main/configuration.h
 main/credentials.h

main/main.ino

@@ -51,6 +51,8 @@ RTC_DATA_ATTR uint32_t count = 0;
 // Application
 // -----------------------------------------------------------------------------
 
+void buildPacket(uint8_t txBuffer[]); // needed for platformio
+
 void send() {
   char buffer[40];
   snprintf(buffer, sizeof(buffer), "Latitude: %10.6f\n", gps_latitude());

platformio.ini

@@ -0,0 +1,34 @@
+; 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
+
+[platformio]
+src_dir = main
+
+[env:esp32]
+platform = espressif32
+board = ttgo-t-beam
+framework = arduino
+
+; note: we add src to our include search path so that lmic_project_config can override
+build_flags = -Wall -Wextra -O3 -Wl,-Map,.pio/build/esp32/output.map -D CFG_us915 -D CFG_sx1276_radio
+; -DLOG_LOCAL_LEVEL=ESP_LOG_DEBUG -DCORE_DEBUG_LEVEL=ARDUHAL_LOG_LEVEL_DEBUG
+
+lib_deps =
+  arduino-lmic
+  TinyGPSPlus
+  ESP8266_SSD1306
+  AXP202X_Library
+
+;  Adafruit ILI9341@1.2.0
+;  AutoConnect
+;  ArduinoJson@5.13.4
+;  Micro-RTSP@>=0.1.6
+; Adafruit-GFX-Library=https://github.com/geeksville/Adafruit-GFX-Library.git
+