Use hyperref to set pdftitle and pdfauthor

For reasons that I do not want to think about orgmode sets the description and
makes sure to credit orgmode as the creator in the pdf metadata but it does not
include the Author or the title. If I was not a lisp weenie I would have set this
in the org file but this works just as well.

Before:

dfc@jumbo:~$ pdfinfo Crypto101.pdf
    Title:
    Subject:    An introduction to cryptography for programmers
    Keywords:
    Author:
    Creator:    Emacs 24.3.1 (Org mode 8.2.6)

After:

    dfc@jumbo:~$ pdfinfo Crypto101.pdf
    Title:      Crypto 101
    Subject:    An introduction to cryptography for programmers
    Keywords:
    Author:     Laurens Van Houtven (lvh)
    Creator:    Emacs 24.3.1 (Org mode 8.2.6)
Bail early
Use GNUism -maxdepth since it works everywhere

Refs #202.
Display a neat error message on exit

Refs #202.
Merge pull request #203 from dfc/pdfmetadata

Use hyperref to set pdftitle and pdfauthor