Implement support for Raspberry Pi 5 using lgpio library

[ohinckel]

This will start adding support for Raspberry Pi 5 using the lgpio libraray (see project or docs).

When building the code the RPI has to be set. The value is now important to specify what to build:

• -DRPI=1 - will build the code for Raspberry Pi 2/3 using the wiringPi library
• -DRPI=5 - will build the code for Raspberry Pi 5 using the lgpio library

Since the code itself is using a RaspberryPi define which is declared when RPI value is set, an RaspberryPi5 define will be declared when the value is set to 5.

At least sending signals using this implementation on a Raspberry Pi 5 is working. The receiving part was not yet tested.

This is related to issue #473.