Update build process to build epi lessons.

* Ignore Rmd files
* Add epi lessons and chunk_options.R to rmd.mk
* Add rmd.mk to Makefile
Knit epi lessons.
Merge pull request #1 from jdblischak/build-epi-lessons

Build epi lessons
index.html
adding pre-bootcamp assessment
adding new instructors
Correcting typos and adding exercise for data structures
Correcting typos and adding wide to long using melt, transform, and
dcast in reshape2
correcting typos and modifying examples and exercises in apply-family lesson
Correcting typos in ggplot2 visualization
Correcting typos and some topics in RR
markdown files for updated R epi lesson
Intro slides
update epi lessons