* Removed setting of `subject` in PDF metadata.
This used to be set to the subtitle, but really the subtitle
need not give the subject. Also, `subtitle` can contain formatting,
so we'd need, at least, a plain text version for this.
* Moved `header-includes` before setting of `\title`, `\author`,
etc. This allows these macros to be redefined.
* Use `\subtitle` command for `subtitle`, instead of tacking it
on to the title as before. We give a no-op fallback definition if it is
not defined. This change should produce much better results
in classes that support `\subtitle`. With the default article
class, which does not define `\subtitle`, subtitles will no
longer be printed unless the user defines `\subtitle` and
redefines `\maketitle`.
* Moved redefinitions of `\paragraph` and `\subparagraph` to
before header-includes.
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