Ensure all examples work and test file matches name of source file

[rjake]

examples for full_argument_names throw errors

full_argument_names(expression(gsub(' ', '_', 'a b c')))
# Error in args(eval(x_fn[[1]])) : could not find function "a_b_c" 

This works though

full_argument_names(parse(text = "gsub(' ', '_', 'a b c')")[[1]])