Fix: Print some descriptive message in this case, e.g. that some required parameters are missing;
Fix: By default, the output directory is cwd + "/dump";
Fix: If the directory (--path) does not exist, the tool should create it and go on;
Fix: fetched the list of collections from the server and dumped the data of all collections if don't give any collection;
Fix: if the user specified a collection name that does not exist.
Fix: print out some progress on screen;
Fix: the tool will print out the JSON returned by the server. Now it print just the error message;