MIPS disassembler refinements (mips1, mips3, psx, rsp)

* Change hexadecimal prefix from $ to 0x ($ means something else in MIPS assembler syntax) and omit for small numbers
* mips1, mips3, psx: Use shorthand mnemonics bal, beqz(l), bnez(l), li, move, neg, negu, not where applicable
* mips1, mips3, psx: Add delay slot to jr ra for stepping out
* mips1, mips3: Remove invalid instructions from other MIPS cores and use .word syntax for invalid instructions
* mips3: Fix field spacing for some instructions

Author: ajrhacker