New hare_err package

All of the error variables were moved out of their respective packages and into a new hare_rec package. This was done to de-couple the errors from their respective datastores. For example, before this change, if you had code that did a Find and that record id did not exist, hare could return a disk.NoRecord or a ram.NoRecord, depending upon which back-end datastore you were using.

Now, hare will return a hare_err.NoRecord, no matter which datastore you are using. Not only is this cleaner, but it makes it possible for your code to check for a specific error by doing a call to errors.Is(err, hare_err.ErrNoRecord). This would not have been possible before since you would have had to write errors.Is(err, disk.ErrNoRecord) or errors.Is(err, ram.ErrNoRecord) depending on which datastore you were using.