Shell escape process arguments that are printed out

Shell escape process arguments that are printed out

cargo build --verbose does output some command lines that cannot be
simply copy and pasted into the shell again. The problem is the
arguments which are output exactly like this: --feature="foo"

When pasted back into the shell, the shell will parse and remove the
double quotes. To counteract this, escape special shell characters when
printing commandlines. Cargo will print --feature=\"foo\" instead, which
can be pasted back into the shell.