Added Collection and Map matchers

[peterklijn]

This PR adds matchers for Collection classes like List and Set and Map classes.

it("CollectionMatcher", () -> {
  final List<String> list = new LinkedList<>();
  final List<String> emptyList = new LinkedList<>();
  list.add("one");
  list.add("two");
  expect(list).toContain("one");
  expect(list).toNotContain("three");
  expect(list).toNotBeEmpty();
  expect(emptyList).toBeEmpty();
  expect(list).toHaveLength(2);
});

it("MapMatcher", () -> {
  final Map<String, Boolean> map = new HashMap<>();
  final Map<String, Boolean> emptyMap = new HashMap<>();
  map.put("one", false);
  map.put("two", true);
  expect(map).toContainKey("one");
  expect(map).toNotContainKey("three");
  expect(map).toContainValue(true);
  expect(emptyMap).toNotContainValue(true);
  expect(map).toNotBeEmpty();
  expect(emptyMap).toBeEmpty();
  expect(map).toHaveLength(2);
});

[mscharhag]

Hi @peterklijn,
thanks for your work :-)

I did a few small changes to your pull request in d49ee6d

• Changed the method name toHaveLength(..) to toHaveSize(..). I think size is the more common term in java for the amount of items in a collection.
• Added generic type parameters to MapMatcher so keys and values can be compared in a typesafe way (instead of Object)
• Changed CollectionMatcher and MapMatcher so they can take null values (similar to StringMatcher).

[peterklijn]

Thanks @mscharhag, happy it's merged :). Good point on the size vs length. I based it on Jasmine, but in Java size is indeed more common.