Interaction between `doorstop create` and `--project`/`-j` is poorly defined and probably buggy

[robtaylor]

doorstop create will always try to create an item at the path given, even if it is not inside the project passed in.

Possible options are - 1) check if the path given is inside the project and error other wise 2) if the path is relative, assume creation at that path from the root of the project, and fail if its an absolute path that is not in the project 3) do it anyway and give a warning.

What was originally intended, and would give the least surprise to current users? @jacebrowning