debugging/toy kernel shell commands

[hawkw]

• dump <STRUCTURE> --- prints fmt::Debug representations of kernel data structures
  • dump idt to dump the interrupt descriptor table (arch-specific on x86)
  • dump gdt to dump the GDT (similarly, x86-specific)
  • dump topo or dump topology to print CPU topology
  • dump heap to print heap metrics (and/or heap maps?)
  • dump memmap or something?
• sleep <TIME> (or something) --- spawn a sleep task for that demo (so we can stop spawning demo sleep tasks by default)
• something to probe PCI devices at an addr?
• maybe a command to set breakpoints?

[hawkw]

bd2f195 and #375 added some simple dump commands, as well as a framework for defining shell commands.

[hawkw]

sleep <SECONDS> command added in #377

[hawkw]

I've implemented a bunch of these, so I'm gonna call this one done. We can open separate issues for the other ones.