Benchmark difference with SmallVec<[u8;31]>

[kevaundray]

Inner nodes can have variable lengths up to 31 bytes. Currently, we are using Vec for this, however we could use SmallVec which would not create a heap allocation until the size goes over 31 bytes.

The downside is that with enough SmallVec's, we may run into stack overflow issues. Also note that accessing the stack will not always be faster than accessing the heap, see https://stackoverflow.com/a/24057744 . Hence, we should benchmark the difference in pathological and non-pathological cases.