eolian: remove pointers from complex and class types

eolian: remove pointers from complex and class types

Complex types (i.e. list, array, hash, accessor etc.) now do not require
pointers with them anymore (the pointer is implied) and the same goes for
class handles. Eolian now explicitly disallows creating pointers to these
as well. This is the first part of the work to remove pointers from Eolian
completely, with the goal of simplifying the DSL (higher level) and therefore
making it easier for bindings (as well as easier API usage).

@feature