a couple fixes

some small mistakes I noticed while going through the code with a fine-toothed comb:

main.c
- POSTSCRIPT_SIZE should be 6, not 4, now that there's a word to store OSCCAL

micronucleus_lib.c
- bcdUSB referring to USB Spec 1.1 is used, instead of bcdDevice, referring to the device release number

Sorry about the whitespace showing up as changed, I don't know how to fix that.