Leverage cmake directory management and targets

[sporniket]

• use -B <path_to_build_folder> to manage build folder, instead of manually creating directory and going there.
• use --target ... to avoid delving into specific subfolder and calling makeinstead of cmake.
• The build folders are created outside of pico-* folders, so that they are not lost among the various subfolders of the pico-examples folder.

[lurch]

Note that pico_setup.sh was originally written to closely mirror the instructions in https://datasheets.raspberrypi.com/pico/getting-started-with-pico.pdf (back from before the Raspberry Pi Pico VS Code extension existed 😂 ), which is probably why it does things "the long way" rather than using "advanced options" ?

[sporniket]

Ho I see.