[#63] A multi-value config get operation

[dmlloyd]

This is a possible implementation of #63.

[dmlloyd]

Many collection classes have a constructor that takes a single integer which is a size hint; these collections types can be passed in using method references. For other cases, where the collection type has a no-arg constructor, there could be a Supplier<C> variant. The method would probably have to have a different name in order to disambiguate cases where the class provides both (which includes ArrayList and HashSet, two choices which are likely to be popular).

I don't think this is really necessary though. The most interesting size-less constructor is probably TreeSet - but in this case it is likely that the user will want to pass in a Comparator anyway.

Here are some usage examples, just using String items:

    List<String> list = getValues("my.list", String.class, ArrayList::new);
    Set<String> plainSet = getValues("my.set", String.class, HashSet::new);
    SortedSet<String> fancySet = getValues("my.fancy.set", String.class, s -> new TreeSet<>(String.CASE_INSENSITIVE_ORDER));

[jmesnil]

having some tests would have been great

[dmlloyd]

"Possible implmentation" went to "final implementation" faster than expected :)

[jmesnil]

eh, that was my impression ;)

I'm adding them

[kenfinnigan]

What can I say, I'm over eager