Improve disassembly of branch instructions

- I kept getting confused trying to read these instructions, so now their
  disassembly looks more MIPS-like:
  * All mnemonics have had 'b' prepended to them for "branch".
  * The CMP_CHECK bit alters the displayed mnemonic for the inverted
    versions. e.g. BEQ can be displayed as BNE.
  * The following JMP instruction that encodes the branch destination has
    been folded into the disassembly of the branch instruction. Unlike
    MIPS, I chose to display it offset from the branch check with =>
    instead of another comma.

src/zscript/vm.h

@@ -193,6 +193,7 @@ enum EVMOpMode
 	MODE_IMMS,
 	MODE_IMMZ,
 	MODE_JOINT,
+	MODE_CMP,
 
 	MODE_PARAM,
 	MODE_THROW,
@@ -209,6 +210,7 @@ enum EVMOpMode
 	MODE_AUNUSED	= MODE_UNUSED << MODE_ASHIFT,
 	MODE_AIMMS		= MODE_IMMS << MODE_ASHIFT,
 	MODE_AIMMZ		= MODE_IMMZ << MODE_ASHIFT,
+	MODE_ACMP		= MODE_CMP << MODE_ASHIFT,
 
 	MODE_BI			= MODE_I << MODE_BSHIFT,
 	MODE_BF			= MODE_F << MODE_BSHIFT,