Adding `CreateTodolistByProject`.
Adding docblock for `BasecampClient#createTodolistByProject()`.
Adding test for `BasecampClient#createTodolistByProject()`.
Adding `getCompletedTodolistsByProject()`, `createTodoByTodolist()`, `createCommentByTodo()`.
Fixing tests.
Testing `getAllTodolistsByProject()`.
Adding attachments.
Fixed test for `createAttachment()`.
Merge pull request #2 from rjkip/api

API additions