* add requirement to use only types T for spin lock, where the behavior Send is specified
* remove obsolete implementation of a irqsave refcell
* replace DoubleLinkedList by LinkedList of the alloc library
* using of the core collection library to handle memory and tasks
* the vector of PCI adapters aren't longer protected by a lock because these adapter are initialized at boot time. Afterwards, we have only read-access.
* Freelist: add check if a reunion with the previous slot is possible

- the logical address space is completly separate from the physical
- consequently, different names are used

- avoids false sharing

* Refactor: Fix Clippy warnings

- Added support for empty println!()
- use short hand initialization when possible
- replace if x==false with if !x
- replace unwrap_or(function_call()) with unwrap_or_else(|| function_call())
- and others

* Update to Rust edition 2018
 - Mostly just adds crate::

- introduce macros to switch between kernel and user space
- add core-specific variable to store the address of the kernel stack
- add task value to store the latest user-space stack pointer

- switch back to the default mm::allocate

- a page guard protect the stack against overflows
- the page before and after stack is invalid and trigger a page fault

- wakeup handler checks if a task with higher priority is available
- if yes the handler calls the scheduler

- increase the readability of the code

- lockless scheduling on a local core
- only the communication between cores is realized with protected cores
- cores use inter-processor-interrupts to trigger a queue check

- clone creates a new TLS
- tbss is completly zeroed

if the idle task wakeups a task, avoid halt state

- create ist0 for every task
- add functions to reschedule within and without an interrupt handler