Behavior of printing whilst compiling using knitr

[abhsarma]

From #118

How to support printing whilst compiling using knitr? Multiverse supports two types of code chunks: r and multiverse. How should each of these behave whilst knitting?

printing using an R code chunk

we have the following options:

1. Print the last evaluation (i.e. the output from the last universe at that point in the code, which may not be the last universe in the overall universe)
2. Do not allow a user to print variables declared from a multiverse code block using r by throwing an error

printing using a multiverse code chunk:

we have the following options:

1. Print an output for each universe. This can get annoying if one is trying to print a data frame and ends up with hundreds of data frames.
2. Do not print anything unless the user is compiling as an emar using the knit_as_emar() function. The knit_as_emar() function will incorporate the necessary tangle widgets which will allow the user to navigate the output of all the universes. If the user is not using knit_as_emar(), simply show the original multiverse code including branch functions but do not evaluate.

[mjskay]

(2) seems reasonable to me when knitting. If you want a single value, either use a {multiverse} block or extract the variable from the specific universe you want and print that in an {r} block... right?