Make sensible property/method naming behavior

[special]

There are a variety of weird rules and behaviors around method and property names. Need to decide what behavior actually makes sense and document it.

• Certain names are disallowed, primarily because the backend QObject uses them. Some of those are fairly generic.
• The first letter is always made lowercase for QML
  • This leads to awkward results for properties like "URL"
• Properties can be renamed with the json field tag
• Setter functions are always set[PropName], with the first letter uppercase
  • Renamed properties from the json tag should use their property name, not field name
• A field tag to explicitly choose a setter function could be handy
• Tags in general should be cleaned up a bit

[rburchell]

This leads to awkward results for properties like "URL"

Qt-side, this would be Url, which would then be lowercased to url -- not a problem. Perhaps the issue is in not respecting the naming rule of not uppercasing an acronym?

[special]

Which naming rule do you mean, exactly?