Crash when enum description keys do not match enum values

[jautor]

A crash occurs within the XML tree library when an enumDescription / LongDescription key does not match a value in the enum list. While this is an error in the input, it would be helpful for the tool to validate that description entries match up with enum values. This can be easily reproduced using the test.json file in the repo, such as:

    "ThingType": "RackMount | Cheap | Expensive | Obsolete | Trendy",
    "ThingType!enumDescriptions": {
        "RackMount": "tmp",
        "SUPERCHEAP": "THIS VALUE DOES NOT MATCH A DEFINED ENUMERATION!",
        "Expensive": "tmp2",
        "Obsolete": "tmp3",
        "Trendy": "tmp4"
    },