Fix indents in opcode.h.
Add comments in opcode.h
Fix comments in opcode.h
make_metaclass should skip MRB_TT_ICLASS; close #1369
Merge pull request #1367 from suzukaze/fix-indent-opcode.h

Fix indents in opcode.h.
Merge pull request #1368 from suzukaze/add-comments-in-opcode.h

Add comments in opcode.h