- makes it easier to work on a solution when you can one-step define the source root containing the example.
- one step toward making it easy to run unit tests against example solutions in CI.

- fixes exercism/x-api#59

Define the missing class (with no content)

Signed-off-by: Vincent Demeester <vincent@sbr.pm>

Added track specific documentation

Change hamming test to throw an exception for different strand lengths

Now throws an IllegalArgumentException if the strands are different
lengths.

merge

Added exercise accumulate

Added exercise atbash-cipher

The other track problems follow this convention as well.