error when running code as is from use_rmarkdown_template

[ljanda-amplify]

If you run the code as given in the default function signature for use_markdown_template(), you encounter an internal function, asciify() and therefore an error, which can be confusing to new users

usethis::use_rmarkdown_template(template_name = "Basic Template",
                        template_dir = tolower(asciify(template_name)),
                        template_description = "the most basic of templates",
                        template_create_dir = FALSE)
#> Error in asciify(template_name): could not find function "asciify"

^{Created on 2019-05-13 by the reprex package (v0.2.1)}

[jennybc]

The problem here is that we are revealing a non-exported helper, asciify(), which is problematic, when we reveal how the default value of template_dir is computed, which is good.

According to the tidyverse principle "Avoid magical defaults", we've decided this is a practice we'd like to avoid.

Two things need to be done:

1. The default value of template_dir should become NULL and, internally, template_dir should be set like so:
   template_dir <- template_dir %||% tolower(asciify(template_name))
2. The documentation of template_dir needs to be updated to reflect that it will be based on template_name, if not supplied.