Add `BINARY_SLICE` and `STORE_SLICE` instructions.

[markshannon]

We want this, because:

• Specializing for indexing by int and by slice are different and should be treated differently
• It avoids creating the temporary slice object.
• Indexing by slice is syntactically distinct from indexing by object. The compiler can generate better code if it has different instructions.

For full discussion see faster-cpython/ideas#319