Clearly state the functions' arguments' names

[Alejandro Catalina]

There are cases where our test suite for markmyassignment checks the functions with some parameter names that must be present in the definition of the student, as in

p_identical_twin <- function(fraternal_prob=..., identical_prob=...) {}

If the student then names the function arguments using a different name R will raise an error, so we should just state cleary in the assignment pdf that they must use those same names.

[Måns Magnusson]

Agree. Should probably check argument names for all functions in all tests.

[Måns Magnusson]

Now fixed and in PR #47 .