fix: trivial typos
enh: tikz usage is now printed using formatR
enh: add reference
cons: use \code in section title
cnt: don't refer too much to TeXlive 2007, it's 2013 now
enh: use microtype
fix: use IfFileExists for xelatexEx.pdf to allow testing compilation
Revert "fix: use IfFileExists for xelatexEx.pdf to allow testing compilation"

This reverts commit 3bedc1e2c730be08a950c8be80c75118db9051b2.
fix: consistently use \lang{R}
fix: use `` '' instead of " for quotes