Fix a bug with ignore params printing a file path even if there are no unused
variables.
Upgrade optimist dependency.
Update usage string, make sure ignore-params is a string.
Print a usage string if user uses --help option or doesn't pass any files to the
command.
Update usage string.
Add some tests for the cli and --ignore-params option.
Merge pull request #10 from Kami/fix_ignore_params

Fix a bug with ignore params printing a file path even if there are no unused variables