Added a few more register bitnames for the SD driver
Added some extra comments to the interrupt handler and context switch code
Changed FAT -> FAT32 in the debug message from the filesystem driver
Tweaked the readme by removing the feature list, as it changes too much
Removed the message saying which syscall is being handled
Added a framework for asynchronous I/O

* The next patch is required for this to work, as IRQ interrupts
  cannot return to SVC mode because the stack pointer is not saved.
  The next patch adds kernel threads which are needed to use the
  new functionality.
Added support for kernel threads, started work on dismantling wagtail::process

* The process class is to be turned into a base class for
  various types of processes. This work has only just begun,
  and support for loading applications still remain in the
  process class. It may not work anymore, though.