* Add defines for LED, button and serial port
To make supporting different board layouts easier, this introduces some new defines:
For all platforms:
- `KNX_LED` - the programming LED, defaults to `LED_BUILTIN`
- `KNX_BUTTON` - the programming button, defaults to `0`
For Arduino platforms:
- `KNX_DEBUG_SERIAL` - the serial port that is used for debugging, defaults to `Serial`
- `KNX_SERIAL` - the serial port used for communication with the TPUART, default depends on platform
* GD32 flash workaround
Addressing #181
At least some GD32 devices seem to require unlocking the flash twice. As the unlock function exits with `HAL_OK` if the flash is already unlocked, STM32 devices can run the same code without issues.
* Add H8I8O and H8C09 configurations to knx-demo
Addressing #181
These configurations both serve as examples for the use of these boards and other custom boards that don't use the standard pinout.
* Add STM32 unlock target
This copies the brute force unlock approach by @pavkriz into a custom target. With this commit, it is possible to automatically unlock e.g. a H8I8O board without leaving the PlatformIO IDE.
See #181
