RISC-V Matrix Multiplication Extension Specification v0.4.0

update logs from v0.3
spec

1. remove matrix-scalar instructions
2. remove matrix-vector instructions which vector operand is indexed by scalar register
3. change misa definition
4. add float pointwise instructions
5. add some integer pointwise instructions
6. add integer float conversion instructions
7. add matrix memory model
8. update pointwise instructions' opcodes
9. fix other minor bugs

demos
add configure examples for cpf

toolchain and simulation tools are still based on v0.3(not updated)