Possibility to specify FFI::Platypus custom type

[pablrod]

NativeCall works very well with FFI::Platypus types, but sometimes is useful to attach custom types. For example: StringArray, StringPointer or char ***.

[mohawk2]

@plicease Thoughts? :-)

[plicease]

It would be nice I am not exactly sure what the interface should be.

[pablrod]

My proposal is enabling two interfaces:

1. Global: function register_type in NativeCall.pm (global means subclass level, maybe using a my %custom_types where the key is caller's __PACKAGE__)

2. Per function declaration:
   Add an attribute called CustomTypes that tries to attach every type name passed