Add cooperative multitasking support

[thomasarmel]

Add support for cooperative multitasking

WARNINGS:

• Each task will have a stack size of 4096 bytes, there is no check if a task overflows this limit
• The maximum number of tasks is set to 10

->If you don't need multitasking, you can disable it (don't forget to remove TASKING = Tasking::init(); in lib.rs)

FURTHER IMPROVEMENTS:

• Automatically switch tasks at clock interrupt (we will need to disable interrupts for sensitive operations like task creation or heap allocation)
• Add support for passing parameters to tasks (like pthread in C)

[thomasarmel]

[thomasarmel]

@o8vm