Add support for Raspberry Pi (and possibly similar boards)

[Caian]

This PR adds the necessary components for micro-ROS compilation on Raspberry Pi boards. This is a simpler, ligther, solution than compiling ROS2 on those platforms, especially older ones like RPi 1 and zero where necessary packages are not available.

I also added an simple transport based on UDP sockets. This transport assumes that the network is already set up on the linux side. This new transport is not tied to the framework, and I changed extra_script.py to point to a generic linux framework.

The wiringpi was added as a supported framework because it is the framework used by Raspberry Pi boards, but in practice Micro-ROS and the new transport do not use it at all, so other linux-based boards may be compatible.