Checks if a file actually is an Rmd file.
check_rmd(fname, verbose = TRUE)
A character string. It is the name of the student submission file.
A logical value that prints messages if a non-rmd file is found.
It runs three checks. First, it checks for the file extension to be Rmd or rmd or any such variant. Second, it checks for a YAML header at the beginning of file. Finally, it checks if there is at least one properly defined R chunk within the file.
The function will return TRUE if all the (3) checks pass, and FALSE otherwise.