Create a project scope

[fulldecent]

Creating a scope to define what contributions this project is looking to accept will help the community to close other issue.

Here is an example of something I think is clearly out of scope:

#428

But I can't convince anybody else of this unless 1) someone with commits access here says so, or 2) I can point to the project scope.

[fulldecent]

Recommended tag: project organization

[fulldecent]

The project scope should include:

• New implementations will be considered only as a pull request with a full working implementation that passes all test cases and works with our continuous integration. Please do not use issues to request new implementations.

This will allow to close issues like this: #428 as out of scope.