Kdb import merge

Brings the merging framework to the import command. I commented all the side_value tests because i couldn't find this value in any testdata. 
The reason I added this line is due to the change of the threeway merger. Initially it didn't merge parentKeys because for most backends this will cause a merge conflict (because the parent key contains the path). In order to retain backward compatibility and not to change the behaviour of the merge command, I remove the parentKey before merging. 

Why is anything lost? Shouldn't kdb.set(merged, root) only modify the Keys inside merged? I have to cut, because of the behaviour of kdb.get (see #57). Is there a better way?