It is no longer necessary to appease multi_json

Multi_json 1.7.5 dropped the stdlib warning, so json can be removed from
the Gemfile as an explicit dependency.
Remove Autotest configuration
Remove Bones configuration
Add a TODO
Add tests for fields of Regress::TestStructC
Add a note note regarding an intermittent test failure
A field of an object type is always a pointer
Array elements of an object type are always pointers
Merge tag_or_class_name with tag_or_class
Handle inline arrays of structs
Tests other GIMarshallingTests functions that use flat arrays of stucts

Now that flat arrays of structs are supported, the tests for these
functions no longer need to be skipped.

The function .gvalue_flat_array_round_trip has the added complication
that it takes GValues by value. This is not yet supported.