I check MIPS microMIPS manual [1], and found the major opcode might
be wrong. I add a comment to explicitly indicate what manual I am refering
to, and according that manual I remove microMIPS32 major opcodes 0x1f.
As for others, like 0x16, 0x17, 0x36 and 0x37, they are for higher-order
MIPS ISA level or new revision of this microMIPS architecture. Quote
from Johnson, they are belong MIPS64 [2].