Imports of ctr command

PathSynopsis
fmtPackage fmt implements formatted I/O with functions analogous to C's printf and scanf.
github.com/mmcloughlin/avo/buildPackage build provides an assembly-like interface for incremental building of avo Files.
github.com/mmcloughlin/avo/operandPackage operand provides types for instruction operands.
github.com/mmcloughlin/avo/regPackage reg provides types for physical and virtual registers, and definitions of x86-64 register families.
syncPackage sync provides basic synchronization primitives such as mutual exclusion locks.