code: protected <T> Iterator<T> providers(Class<T> pCategory) {
          return getRegistry(pCategory).providers();
      }
docs: Returns an {@code Iterator} containing all providers in the given
  category.
  <p/>
  The iterator supports removal.
  <p/>
  <small>
  NOTE: Removing a provider from the iterator, deregisters the current
  provider (as returned by the last invocation of {@code next()}) from
  {@code pCategory}, it does <em>not</em> remove the provider
  from other categories in the registry.
  </small>
  
  @param pCategory the category class
  @return an {@code Iterator} containing all providers in the given
  category.
  @throws IllegalArgumentException if {@code pCategory} is not a valid
  category in this registry