updated RISC-V specs

https://blog.riscv.org/2015/11/risc-v-draft-compressed-isa-version-1-9-released/

Click to access riscv-compressed-spec-v1.9.pdf

A. Waterman, Y. Lee, D. A. Patterson, and K. Asanović,

“The RISC-V Compressed Instruction Set Manual, Version 1.9,”

EECS Department, University of California, Berkeley, Tech. Rep. UCB/EECS-2015-209, 5 Nov 2015.