Separate MK.. macros (in opcode.h) to machine.c
Obey coding conventions
Add machine `nios'
Add cross-compile setting for Nios2
Rename cross-compile build name
Modify MKOPx/GETARGx macros (add mrb_state*)
Add toolchain setting for Nios2
Split machines.c to machines_xxx.c
Support variable-length instruction

(codedump is disabled now...)
Fix generating wrong immediate value of OP_LOADI
Add machine type 'rubic' to default build
Fix NiosII opcode width
Support rubic code dump
Remove warnings and fix bne instruction
Pass r31 when OP_ENTER