Fix merge conflict in uart.c
Fix more sloppy merge errors
Added os_memset, os_strchrnul, os_strlen, os_strtok, os_strspn, os_strcspn

These new functions were adapted from MUSL
Added strcpy from MUSL

Also moved some functions around in klibc.c
Appended "os_" to strcpy to make it "os_strcpy"
Merge branch 'klibc' of https://github.com/rellermeyer/course_os into argparse

Conflicts:
	kernel/Makefile
	kernel/start.c