Clearer deliniation illustrative and live vignette code

[athowes]

Hi! Have just been reading through the EpiEstim Vignette to learn about the package.

One thing that I thought could help make things clearer is to make it quite obvious which code snippets are just there for illustrative purposes, and which can be run by someone working through the vignette to generate the displayed outputs.

It would also be nice in the sections that the user should be able to run to make it easier for them by having all code availabe. For example within Example A: Entire Workflow loading the data could be added to the displayed code.

Note: perhaps this is just my preference, as I like to try to code along while reading, and to others it matters less!