Handle misalignment properly in jump-link instruction

[chiangkd]

From spec, an instruction-address-misaligned exception is reported on the branch or jump instruction, implying rd would not be updated.

For simplicity, I keep do_jump function to handle branch instruction, and modify only op_jump_link function.

Reference: https://riscv.org/technical/specifications/ (section 2.2)

[jserv]

In addition, use plain text in git commit messages rather than markdown.

[jserv]

Thank @chiangkd for contributing!