Add support for singleton resources (AEP-156)

[mkistler]

The current rules for the standard methods do not properly exclude "singleton resources" (AEP-156) and thus may generate false positives for singleton resources that comply with AEP-156. False negatives are also possible.

For example, a get for a singleton resource will be a GET method on a path that ends in a (singular or plural) static path segment. The rules for AEP-132 (Standard List Operations) will confuse this operation with a list operation and likely fire false positives, such as requiring the operationId to have the form "List".

A negative example is that the rules for AEP-131 will not recognize a get for a singleton resource as a "Standard GET" and so will not check for the body containing a resource.