luhn: update to latest canonical tests

Issue #154: make journey-test.sh use exercises

Issue #276: linked-list: Rename Deque to DoublyLinkedList

Previously this code was applying the required operations to every
second digit starting from the LEFT. The correct solution applies the
required operations to every second digit starting from the RIGHT. The
fact that this was not caught by the tests is a problem! The canonical
tests have been updated since this exercise was last overhauled, so next
steps should be to update to match the expanded canonical test suite,
then test against a broken implementation to see if it is now caught.
Even if it is, it may be worth including an explicit left vs right test
in the canonical suite if one does not already exist.

Issue #261: Bring phone-number exercise in to compliance with canonical data

Changed names of tests to be consistent and changed the order
so that similar tests are grouped together. Added more tests
using the canonical data.

Issue #284: add Ignore annotation to etl tests

* hello-world: Modify tests to reject name == "" comparison

* hello-world: Add emptyStringIsComparedByValue() test case

perfect-numbers: add to track

* Add Gitter badge

* Issue #253: Tried to improve grade school structure. Removed .db() function, added numberOfStudents functions and renamed the sort function to studentsByGradeAlphabetical. Added test to check that grade() gets the students in the order they were inserted. Removed getsStudentsInAGrade() test as what it was testing was already being covered by the tests before it.

* Added tests for protection agains mutation of the list object

* Issue #253: Make the sort test more generic. This to allow a broader range of implementations. Currently users are hindered into return the type HashMap<Integer, List<String>. This test update will check the order of any Map that maps to any Collection value type. This opens the doors for more possible types of solutions.

* dibs: I will implement exercise Clock

* Implemented clock exercise

* Issue #253: Tried to improve grade school structure. Removed .db() function, added numberOfStudents functions and renamed the sort function to studentsByGradeAlphabetical. Added test to check that grade() gets the students in the order they were inserted. Removed getsStudentsInAGrade() test as what it was testing was already being covered by the tests before it.

* Added tests for protection agains mutation of the list object

rectangles: polish example implementation

luhn: update tests and sample implementation

Phone number exceptions

Use an @Rule instead of @Test(expected=…)

Fixes #252. Passing invalid input to the constructor should now expect
an IllegalArgumentException.

Fixes #245.

Tracking issue: https://github.com/exercism/x-common/issues/491

dibs: I will implement exercise Matrix