Examples have previously relied on the (really: some) nightly toolchain
to be the default. As that, in practice, is a problematic assumption,
the latest toolchain to use is now determined programmatically, and that
is set explicitly on the examples that use nightly.
Workaround-For: https://github.com/rust-lang/rustup/issues/3015
On microbit-v2, getting .well-known/core would otherwise result in a
stack overflow.
Consequently, some boards were removed from the list of supported boards
as the currently required RAM exceeds their capacity.
