Update the docsting of core functions

docs/src/core.md

@@ -9,10 +9,8 @@ CUTEst in Fortran defines functions called with `cutest_u*` or `cutest_c*`,
 for the unconstrained and constrained cases, respectively.
 For each of those, we dropped the `cutest_`, so the functions `cutest_ufn` and
 `cutest_cfn` are available as `ufn` and `cfn`.
-To use then you have to convert the types using `Cint` and `Cdouble`, and
-pass arrays because of the underlying pointers in Fortran.
-In practice, there isn't much improvement in calling these or `ccall`s, except
-for the use of the internal `cutest_lib_double`.
+It allows to have a unified interface for the routines in single, double and quadruple
+precision.
 
 **Only use these functions if you really know what you're doing.**