* Added `customWorkingDirectory` and `useCustomWorkingDirectory` properties to `Scheme.Run`
* Use new `customWorkingDirectory` and `useCustomWorkingDirectory` when generating `XCScheme.LaunchAction`
* Updated ProjectSpec.md to document new `customWorkingDirectory` and `useCustomWorkingDirectory` properties
* Fix for not setting customWorkingDirectory in the toJSONValue function
* Added test to make sure usCustomWorkingDirectory value is true when the customWorkingDirectory is set to non nil
* Change to infer the value of SchemaGenerator.LaunchAction.useCustomWorkingDirectory based on the value of Schema.Run.customWorkingDirectory
* Removed useCustomWorkingDirectory from the project spec now that it is no longer user defined.