0.3.0.0

• Has-classes and a lens for Engine and refactored optics
• Eq instance for Engine (in case multiple engines are running)
• change representation of MStruct to Data.Map.Strict from list of pairs; added related Iso
• safe get-functions
• convenience function: mxArrayGetFirst
• ability to use MStruct as function arguments
• utility type and converter for varargs
• cellFromListsIO for interop with lists of strings
• fromListIO convenience function
• more tests
• stack support
• nix support