Add EnumerableField<T>

[jwienekamp]

This enables using IEnumerable<T> on input and output models. On input models there is no difference to using arrays.

On output models the rows will be returned one-by-one using yield return. Rows are loaded from SAP individually with each iteration on the enumerable. This enables very large datasets to be handled without everything to be loaded into memory all at once.

In conjunction with InvokeFunction of pooling, the generated function now has to be stored and not disposed immediately. Otherwise the tableHandle would be destroyed on SAP side and calling any interop method using this handle will throw RFC_INVALID_HANDLE.

[campersau]

In conjunction with InvokeFunction of pooling, the generated function now has to be stored and not disposed immediately. Otherwise the tableHandle would be destroyed on SAP side and calling any interop method using this handle will throw RFC_INVALID_HANDLE.

This would also make it possible to use #55 with pooling.

[huysentruitw]

Awesome addition !