Implement simple virtio9pfs driver

bufio: allow to borrowread up to last byte

Don't error when reading from end of tar file

hash: import from Hare stdlib

Makefile: update for upstream hare changes

sysinit: provide usrinit will all system memory

build: move SYSLINUX to config.mk

Fix my name

rt: overhaul memory allocator

Functionally identical but with much more readable code.

sysinit: move file objects onto heap

This will make freeing them up easier later on.

rt: fix various allocator and mmap issues

Large mappings spanning >64 pages could be mapped non-continuously,
particularly if there were other threads doing allocation at the same
time.

rt: implement spinlocks and simple atomics

Updates malloc and free to acquire a spinlock before entering critical
sections, and updates mmap to use atomic fetch_add to update the heap
break.

Further improvements will be necessary to have a complete story for
thread safety in Mercury, namely the reduction or elimination of static
variables in the stdlib (e.g. strconv).

References: https://todo.sr.ht/~sircmpwn/mercury/13

all: improve error handling further

usrinit: implement simple serial terminal

Last pieces for usrinit threads touching up

rt: complete basic threads implementation

sysinit: basic TLS support

Basic because processes which want to spawn threads still have to have
access to a lot of capabilities, including some spare memory and their
own vspace and task -- future improvement will create an IPC protocol
for managing threads so that this is not necessary.

sysinit: implement procmgr::query

Still todo:
- Add sysinit itself to the list of processes
- Set up usrinit via procmgr instead of munging it

usrinit: add help command

usrinit: add cat, hexdump commands