H8I8O (#209)

* 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

examples/scripts/stm32rdu.py

@@ -0,0 +1,34 @@
+#!/usr/bin/env python
+from subprocess import run
+from datetime import datetime, timedelta
+from os.path import expanduser
+
+ocddir = expanduser("~/.platformio/packages/tool-openocd/")
+chip = "stm32f1x"
+
+def unlock(*args, **kwargs):
+  print("Please connect the board within the next two minutes.")
+  endtime = datetime.now() + timedelta(minutes = 1)
+  ret = 1
+  while ret != 0 and datetime.now() < endtime:
+    ret = run(["bin/openocd", "-f", "interface/stlink.cfg", "-f", "target/" + chip + ".cfg", "-c", "init", "-c", "reset halt", "-c", chip + " unlock 0", "-c", "reset halt", "-c", "exit"], cwd = ocddir).returncode
+  if ret != 0:
+    print("Timeout")
+  return ret
+
+try:
+  Import("env")
+except NameError:
+  import sys
+  if len(sys.argv) > 1:
+    chip = sys.argv[1]
+  if len(sys.argv) > 2:
+    ocddir = sys.argv[2]
+  unlock(None, None)
+else:
+  ocddir = env.PioPlatform().get_package_dir("tool-openocd")
+  options = env.GetProjectOptions()
+  for option in options:
+    if "unlock_chip" == option[0]:
+      chip = option[1]
+  env.AddCustomTarget("unlock", None, unlock)