Add rename()

[pfrazee]

Atomic method to rename a file or directory (thus moving children)

[freddi301]

some ideas and questions about implementation:

• is there any transaction like mechanism?
• is there any lock like mechanism?
• the metadata feed is this.db in https://github.com/hypercore-protocol/hyperdrive/blob/master/index.js?
• if there is no transaction or lock mechanism, the atomic rename could be implemented as a batch operation on metadata hyper-trie?
• if so, do we need to wait/lock some files/directories, compute the whole batch, run it, and then unlock?

Renaming a file source target

• copy paste stat this._putStat(target, this.lstat(source))
• this_del(source)
• what are the guarantees of linux rename syscall for a file?
• need to check if target is not already existing?
• need to check if source file is opened?

Renaming a directory

• copy paste stat this._putStat(target, this.lstat(source))
• iterate recursively on every child
• this_del(source)
• what are the guarantees of linux rename syscall for a directory?
• need to check if it's a mounted drive?