Fix/inline begin function

[mcelb1200]

Bug Report: Multiple definition of BLEMIDI_ESP32::begin when using with ESPAsyncWebServer

Description:

When using the lathoub/BLE-MIDI library in a PlatformIO project with ESPAsyncWebServer, a "multiple definition" linker error occurs for the BLEMIDI_ESP32::begin function. This is because the function is defined in the header file hardware/BLEMIDI_ESP32.h, and this header is included in multiple source files.

Test and logs at
ble-midi-repro.zip

To Reproduce:

1. Create a new PlatformIO project for the esp32doit-devkit-v1 board.
2. Add the following libraries to platformio.ini:

   lib_deps =
       lathoub/BLE-MIDI
       me-no-dev/ESPAsyncWebServer
       me-no-dev/AsyncTCP
       fortyseveneffects/MIDI Library@^5.0.2

3. Create a main.cpp file with the following content:

   #include <Arduino.h>
   #include <BLEMIDI_Transport.h>
   #include <hardware/BLEMIDI_ESP32.h>
   #include <MIDI.h>
   #include <ESPAsyncWebServer.h>
   
   AsyncWebServer server(80);
   
   BLEMIDI_CREATE_DEFAULT_INSTANCE();
   
   void setup() {
     Serial.begin(115200);
     MIDI.begin();
     server.begin();
   }
   
   void loop() {
   }

4. Create a second source file other.cpp with the following content:

   #include <Arduino.h>
   #include <BLEMIDI_Transport.h>
   #include <hardware/BLEMIDI_ESP32.h>
   #include <MIDI.h>
   #include <ESPAsyncWebServer.h>
   
   void dummy_function() {
     // This function is intentionally left blank.
   }

5. Build the project. The build will fail with the following "multiple definition" linker error:

   /home/jules/.platformio/packages/toolchain-xtensa-esp32/bin/../lib/gcc/xtensa-esp32-elf/8.4.0/../../../../xtensa-esp32-elf/bin/ld: .pio/build/esp32doit-devkit-v1/src/other.cpp.o: in function `bleMidi::BLEMIDI_ESP32::begin(char const*, bleMidi::BLEMIDI_Transport<bleMidi::BLEMIDI_ESP32, bleMidi::DefaultSettings>*)':
   

/app/ble-midi-repro/.pio/libdeps/esp32doit-devkit-v1/BLE-MIDI/src/hardware/BLEMIDI_ESP32.h:125: multiple definition of `bleMidi::BLEMIDI_ESP32::begin(char const*, bleMidi::BLEMIDI_Transport<bleMidi::BLEMIDI_ESP32, bleMidi::DefaultSettings>*)';
.pio/build/esp32doit-devkit-v1/src/main.cpp.o:/app/ble-midi-repro/.pio/libdeps/esp32doit-devkit-v1/BLE-MIDI/src/hardware/BLEMIDI_ESP32.h:125: first defined here
collect2: error: ld returned 1 exit status

*** [.pio/build/esp32doit-devkit-v1/firmware.elf] Error 1
```

Fix:

The fix is to declare the BLEMIDI_ESP32::begin function as inline in hardware/BLEMIDI_ESP32.h. This allows the compiler to resolve the multiple definitions at link time.

Change:

--- a/src/hardware/BLEMIDI_ESP32.h
+++ b/src/hardware/BLEMIDI_ESP32.h
@@ -122,7 +122,7 @@
     }
 };
 
-bool BLEMIDI_ESP32::begin(const char *deviceName, BLEMIDI_Transport<class BLEMIDI_ESP32> *bleMidiTransport)
+inline bool BLEMIDI_ESP32::begin(const char *deviceName, BLEMIDI_Transport<class BLEMIDI_ESP32> *bleMidiTransport)
 {
     _bleMidiTransport = bleMidiTransport;