Fix issues with creating pdf and ps documents, from Carl.

Fix issues with creating pdf and ps documents, from Carl.

cmu-user.tex:
o Include ifpdf package

design.tex:
o Include ifpdf package
o Remove the home-grown ifpdf macro.

macros.tex:
o Remove the home-grown ifpdf macro.

introduction.tex:
unicode.tex:
o Use \url instead of \href for URLs.