Add package `auctex`

* Configure the view program on Mac. The setting should be available on
  AUCTeX master branch, but it is not available on 11.87.3.
  See 1d0d1ac642e1acc6db859458dfcb7a151d657ac1.
* Set TeX-engine and TeX-PDF-mode. Reference:
  http://tex.stackexchange.com/a/26387