memkv

1. Replace filepath library by path library 2. Update Go version to 1.8

List gets mixed-up if a leaf node and a dir node has the same prefix. Added the necessary condition and extended the tests to demonstrate the error. Note: I found this using "confd" with etcd backend were the "ls" function produced a rather unexpected result

I actually encountered this issue when using confd (which depends on this) with etcd as a backend. Since etcd flattens directories, you can end up with a number of keys that are a section of a potentially deeper path. The behavior I was expecting was based off the etcd documentation for since I couldnt find anything in this repo, so hopefully this is correct: Returns all subkeys, []string, where path matches its argument. Returns an empty list if path is not found. Given the keys (like how etcd would structure them): Before this change, if I tried to list all of the keys in the directory, I would get a list with two items - when I would expect the output to be: as they are located in the path. Example program I used to test this change: