Fix tests, allow multi vary across, rename rmd functions to docs

[tiffanymtang]

• Remove print.tbl output from snapshot tests
• Change rmd to docs for consistency. Includes renaming create_doc_template() to init_docs(), create_rmd() to render_docs(), and set_rmd_options() to set_doc_options()
• Allow for varying multiple DGPs/Methods at once in vary_across

[jpdunc23]

Looks great!

My only suggestion is to add back create_rmd, create_doc_template, and set_rmd_options for backwards compatibility. These can just be simple wrappers around render_docs, init_docs, and set_doc_options that output a warning, e.g.:

warn("create_rmd is deprecated and will be removed in a future version. Please use render_docs instead.")

In case you hadn't see warn yet, it's in https://github.com/Yu-Group/simChef/blob/main/R/signals.R, and just wraps rlang::warn.

Perhaps better yet, we could use the lifecycle package instead. See here: https://lifecycle.r-lib.org/articles/communicate.html#rename-a-function. If you feel like doing this, great, but no pressure; we can just use warn for now. But if you do go with lifecycle, then let's use "0.1.0" for the when argument to deprecate_warn.

[jpdunc23]

See #126 (comment)

[tiffanymtang]

Thanks for the suggestions! I added the backwards compatibility using lifecycle