Add BuxtonArray

BuxtonArray is a dynamically allocated self-managing array, which is
also reusable. We can use the BuxtonArray (made easier via its len
member) to easily deal with lists of BuxtonData's, for instance.

This will primarily be used to easily facilitate the listing of keys
within a given layer in Buxton.

Signed-off-by: Michael Ikey Doherty <michael.i.doherty@intel.com>
test: Add test case for BuxtonArray

Signed-off-by: Michael Ikey Doherty <michael.i.doherty@intel.com>