header.tex

\usepackage{multicol}
\usepackage{graphicx}
%% \usepackage[symbol]{footmisc}
%% https://tex.stackexchange.com/questions/826/symbols-instead-of-numbers-as-footnote-markers
\renewcommand*{\thefootnote}{\fnsymbol{footnote}}
%% \renewcommand*{\thefootnote}{\fnsymbol{footnote}}

\usepackage{url}
\DeclareGraphicsExtensions{.png,.pdf,.jpg,.mps}
\newcommand{\cemph}[1]{{\color{red} #1}}
\newcommand{\bemph}[1]{{\color{blue} #1}}
% https://stackoverflow.com/questions/20847371/two-column-layouts-in-rstudio-presentations-slidify-pandoc
\def\begincols{\begin{columns}[T]}
\def\begincol{\begin{column}}
\def\endcol{\end{column}}
\def\endcols{\end{columns}}
\def\twocols{\begin{multicols}{2}}
\def\endtwocols{\end{multicols}}

\titlegraphic{\includegraphics[width=2cm]{maclogo.png}}