Checks if a list satisfies the requirements to be considered a valid b_coding
check_b_coding(b_coding)the unmodified list for convenience
a named list
Checks for...
input being a list
list is of length three and provides the names "column", "u_name_value", "l_name_value",
if b_coding$column provides a single string
if b_coding$u_name_value and b_coding$l_name_value provides a single named value of type character or numeric, and that both are of the same type