Array functionality unimplemented in move

[egroge]

The libra target has support for storing arrays as libra vectors but not accessing them or storing to them. Full functionality was implemented previously, but this was before libra updated to have generic vector data types. Array values should now be accessed using the Vector.borrow() and Vector.borrow_mut() methods, depending on whether the value should be mutated or not, as shown in this example from the Libra testsuite.