Provide overload of wrap_results that does not need a result_map

[ryanmrichard]

PropertyType<T>::wrap_results takes two arguments the results map that it is adding the results to and the results to add to the map. The motivation for taking the results map is that it supports concatenation of multiple property types' results into a single result map; however, when there is only a single property type (or equivalently it's the call to the first of several property types) this leads to code like auto rv = results() to make the initial result map. We should create an overload of wrap_results that does not require a results_map.

Note: this will likely require SFINAE to pull off as the resulting signature will be fully templated.