Created a lesson plan and a concept map for the R package gglot2.
Added faceting exercise for ggplot2 and fixed some typos.
Added the script which contains the answers to the ggplot2 exercises.
Merge branch 'master' of github.com:swcarpentry/boot-camps into ggplot2-pr
Merge pull request #178 from jdblischak/ggplot2-pr

new ggplot2 materials from jdblischak