make_filename: Generate FARS filename for a given year
In rwpalin/fars: Summarize and plot FARS accident data

make_filename() accepts a year input and returns a filename of the form "accident_[year].csv.bz2".

1	make_filename(year, internal = TRUE)

`year`	Integer value representing a year. Inputs that do not coerce to integer will generate an error. The input can also be an integer vector of multiple years.
`internal`	Logical value indicating whether or not the package example data is used. Defaults to TRUE.

Returns a string filename for each valid year, or a coercion error.