addition of template-mutability extension

[Lcfvs]

[mamund]

Since this extension has two properties which have a relationship between them, we should also make explicity how to handle msgs that have one or both properties missing and/or one or both properties with an invalid value.

I think the easiest way to handle this is to explicitly state how message consumers should treat responses (e.g.)

• When the mutability property is missing or contains an invalid value, the response SHOULD be treated as if mutability is set to true.
• When the readOnly property is missing or contains an invalid value, the response SHOULD be treated as if readOnly is set to false.
• A response MUST NOT be rejected if one or more of the properties in this extension is missing or the value is invalid.

Feel free to mod your extension as you see fit.

also, be sure to post a message to the forum to announce the extension and ilicit feedback.