Add convenience methods for creating List, Map valued ObjectReaders (ObjectMapper.readerForListOf())

[cowtowncoder]

One case where helper class TypeReference is often needed is for code like:

List<ValueType> values = mapper.readerFor(new TypeReference<ValueType>() { })
    .readValue(source);

and similarly for Maps. It should be easy to allow a short-cut like:

List<ValueType> values = mapper.readerForListOf(Value.class)
    .readValue(source);
Map<String, ValueType> valueMap = mapper.readerForMapOf(Value.class)
   .readValue(otherSource);

similar to what jackson-jr exposes.