Implements TyrFrom for Deque from array

[hicklin]

Fixes #522.

Ideally, this PR is updated after PR #521 is merged to simplify the tests.

This PR implements the TryFrom trait for creating a Deque from a slice.

Note the use of unsafe for copying all bytes from the slice to the Deque buffer after ensuring that the Deque buffer has enough space.

Also note the use of ManuallyDrop to ensure that any heap memory referred to by the element contents is not dropped at the end of this method since the elements in the Deque buffer will be pointing to it.

[newAM]

I wont be able to properly review this for a bit, wanted to highlight a couple typos until then.