prototype of xtaak.h
add .gitignore
define constructor of CodeGenerator
add errors ERR_CANT_PROTECT and ERR_CANT_ALLOC.
implement Allocator
add Operand and Reg
initialize regs in CodeGenerator()
implement part of CodeArray
allocate protected memory area in CodeArray()
add CodeArray destructor
32-bit friendly
add ERR_NOT_IMPL
add isREG() and getIdx() to identify register
add mov(pc, lr) for debug