More higher order functions for R.

Documentation for package ‘hof’ version 0.1

Ask	Apply logical predicate to vector.
call_fun	Call a function.
failwith	Modify function to return default value on failure.
guard	Modify function to guard against incorrect inputs.
pluck	Pluck a value out of a list.
remember	Creates a function that remembers all invocations.
tee	Tee: report arguments and results whenever a function is called.