tidy = FALSE to preserve code formatting

Created file to hold global chunk options. Specifically this is to set
the chunk option tidy to FALSE, which means code chunks will appear
exactly as written in the RMarkdown file. Each RMarkdown file sources
this file with the global chunk options making it easy to change the
behaviour of all the lessons at once. I added the chunk which sources
this file to all the RMarkdown files using the following command:

```
find full-R-bootcamp/ -name "*Rmd" -exec sed -i 1i'\`\`\`{r, include = FALSE}\nsource("../chunk_options.R")\n\`\`\`' {} \;
```