Provide default argument to prevent error if no options.yml file exists

[ephphatha]

When running manage-ice.rb in a newly cloned repo no default options.yml is provided. This causes the script to throw an error on the {}.merge(opt) line in the Murmur::Ice::Meta constructor unless the user creates a dummy options.yml with at least one key: value pair despite the constructor providing sensible defaults.

[cheald]

Thanks!