Manage Calendars per Project

For projects in which you don´t have a fixed planning, (i.e, 2 days one week, 3 days the next week, or, monday and tuesday this week, thursday and friday next week, etc.) it would be extremely useful to be able to have a calendar related to each project since this kind of project behaviour can be easily managed by creating holidays on the days you wont be working in the project. Otherwise you need to create a weekly plan for each activity which in some cases may turn just painful to plan.