scripts: add copy-examples
scripts: add copy-examples

This is a preliminary script to copy example code from a Markdown file
into a crate's example directory.

This is intended to be used for the upcoming libripgrep guide, but we
don't commit any examples yet.

BurntSushi/ripgrep,BurntSushi/ripgrep,BurntSushi/ripgrep,BurntSushi/ripgrep