Support for the string key which is larger than 32B

[baotonglu]

The paper claims that "For variable-length string key, PACTree stores a maximum of 32-byte key and an 8-byte value in a node. For larger key and value size, we store the partial key in a node then store the rest of the key and values out of the node."

However, I do not find the corresponding implementation in the repo. The current implementation only supports the key up to 32B.