Ensure that TypeMap.map_basic_type always returns a symbol
Improve method name
Make TypeMap.type_specification_to_ffitype the same as map_basic_type

By adding #put_bool and #get_bool to FFI::Pointer, the need for two
mappings was removed.
Add some notes regarding type size
Remove specialized pointer conversion functions
ArgHelper.ptr_to_typed_array no longer needs to handle bare FFI::Enum
Make TypeMap.type_specification_to_ffitype handle structs and enums
Fix element size calculation for GArray
Remove outdated TODO
Skip test for array_struct_value_in if it is not available