Update combines code for A10 and A20 versions; allows changing partition 1; allows forcing write

1. Produces nand-part and nand-part-a20 for A10 and A20 nand MBR formats.
2. Allows changing partition 1 offset/size/name if an integer offset is specified before the first partition info.
3. Backwards compatible argument format with previous version (leaves first partition intact).
4. -f option forces write of MBR, bypassing sanity checks (for recovery).
5. Various fixes/improvements to the output.