pub fn install_dir(exe: Option<&Path>) -> Option<PathBuf>Expand description
The directory to install into, given this process’s own executable path.
None when it cannot be resolved or has no parent, which leaves
MIRA_INSTALL_DIR unset and the script on its /usr/local/bin default —
the right fallback, because a mira that cannot find itself is more likely to
be a test harness than a real install.