Add mechanism for cloning examples into their own crates

[lulf]

No description provided.

[lulf]

@ctron With this, you can run

cargo xtask clone examples/stm32l0/lora-discovery /path/to/new/project

For all the examples to generate one that has the git dependencies setup correctly. The reason for not using cargo-generate is that I couldn't use it with existing examples, so this way is easier to maintain.

[lulf]

bors r+

[bors]

Build succeeded:

• build
• examples