Need More Exercises implemented for Core Path

[Stargator]

See #38 for what a PR that adds a new exercise covers.

General Overview:

• Choose a problem from problem specifications repo
• See this list sorted by exercises implemented by most other Exercism tracks
• Recommend looking for a problem that would fit for someone new to the language and complements the other existing problems (ie: tackles different topics)
• Create a directory in exercises/ for the new exercise
• Update the config.json by including the new problem, outlining the topics it covers, labeling it as "core", assigning an initial difficulty score (See this discussion for how the current scores were considered, and place it after the last exercise.
• To run the tests, execute pub run test from the root directory of exercism/dart

[devkabiir]

@Stargator I am actively learning dart and would like to contribute multiple exercises, i can implement a lot of the exercises. Should i start by creating new issues for the "core" exercises that are yet to be implemented?

[Stargator]

@kabiir There are no universal "core" exercises except for those the maintainers say are. And except for hello-world, that's pretty universal :)

Feel free to start implementing some exercises and include them in an order you think is right and we can discuss it in the PR in more depth.

[Stargator]

Considering we got 10 exercises, I think we have the core finished. Closing.