First bug fixes to get standard XMODEM working (to some extent)
First bug fixes to get standard XMODEM working (to some extent)

Fixed:
- first block starts with number 1
- make it easy to change the start block number if needed
- add filler to the packagedBuffer in case the starting block is bigger than 0 (this allows to maintain the easy array addressing)
- fix hex to dec number
- fix the method of standard checksum calculation

Known to be broken:
- CRC calculation
- Not supporting block numbers that go over 256

exsilium/xmodem.js