Missing a create board method

[albcl]

Issue

There is a missing (and rather useful) method to allow users to create new boards at ease.

mutation {
    create_board (board_name: "my board", board_kind: public) {
        id
    }
}

Solution

I have implemented such a simple function to let us create a board with an optional parameter to determine its workspace.

create_board(board_name, board_kind [, workspace_id])

Pull Request (#60) created

Others

• Tests included.
• Readme updated.