Allow for specification of output file or directory

[joelnitta]

I keep my slides in a different directory that the lesson directory, so I'd like to be able to save the slides elsewhere.

Example code:

CarpentriesSlides::make_md("~/repos/shell-novice", md = "~/repos/shell-slides/slides.md")

[multimeric]

I originally had it work like that, but changed it for simplicity.

How about an API where each function returns the output path, which is auto generated if not provided?

make_md(repo)
# "~/repos/shell-novice/slides.md"
make_md(repo, output = "~/repos/shell-slides/slides.md")
# "~/repos/shell-slides/slides.md"

[joelnitta]

Sure, I like returning the output path (for use with {targets}, actually...)