added log files to gitignore
changed target to axiom instead of test

nicer to run the script with make axiom rather than make test
callback in startServer takes an error paramter
better var declaration

each variable gets its own var declaration, they are also sorted
alphabetically, declared variables on top to avoid hoisting surprises
added some details in package.json
some formatting changes
added a simple input validation utility
added validator to dependencies and removed mongodb driver
added callback counter for follow and listen
added a queue class to handle callbacks to user registry
changed "tags" to "genres"
added documentation and clearer error handling
added documentation
final commit
renamed file for user registry
added validation and changed the getUser logic

accommodated the getUser requests to comply with the new interface
introduced callback scheduler + documentation

changed how getUser handles requests by queuing callbacks rather than
returning reference to user objects
added validation and changed the getUser logic + documentation
changed rating formula + new gerUser logic + documentation
updated QnA