implemented ROUND math routine, corrected some others

STATUS.md

@@ -196,6 +196,7 @@ Floating point mathematical routines - not official, but well known and broadly
 | `$BBD4`   | `MOVMF`      | NOT DONE | copy FAC1 to memory location, rounds if asked      |
 | `$BBFC`   | `MOVEF`      | NOT DONE | copy FAC2 to FAC1                                  |
 | `$BC0F`   | `MOVFA`      | NOT DONE | copy FAC1 to FAC2, skips rounding                  |
+| `$BC1B`   | `ROUND`      | PARTIAL  | not tested                                         |
 | `$BC2B`   | `SIGN`       | NOT DONE | evaluate FAC1 sign                                 |
 | `$BC39`   | `SGN`        | NOT DONE | evaluate FAC1 sign, to FAC1                        |
 | `$BC58`   | `ABS`        | NOT DONE | absolute value                                     |