add diffing HEAD to a sha
bumping version
fixed and issue with the diff function where delete changes were not being added to the output list because the node returned was none as there is no associated data blob with deleted files
change store.get to use and return the commit_sha if returning a tree object
added except to catch NotTreeError so that method does not blow up when the shaw given to look up a tree does not return a tree the method called to look up and object in a git tree throws an exception if the object returned is not a tree
* changed the diff() function to take the commit sha's parent's tree sha and the current commit's tree sha...this saves us the look up and allows us to only compare the commit's p
arent tree with the current commit tree. Without this the look ups were a bit slower.
backing out the last change will fork to add change to diff function
Add overwrite flag to herodb put calls.  If this flag is set to true and an object is being put, then take the fields in the object and overwrite the existing fields and also remove any existing fields not in the incoming object.  This will only do a shallow replacement so child objects will not be affected.
Change commit message for PUTs to only include fields that have changed.