The Smarty API for compiling templates don't return any meaningful error
status if a template fails, so we buffer the output and scan it for
error messages instead. If we find one, we return a non-zero error code
to signal the error to the shell or calling process.
Also added more detailed copyright headers.
The Smarty class is in the Smarty namespace, and should not be loaded
manually, but through composer. This is taken care of by requiring
`boot.php`. Also make the script slightly more robust as to where it is
invoked from.
