Write hex file with chooseable byte count

[erki1993]

At the moment the only possible data field byte count is 16 when using write_hex_file.

Intelhex wiki: The maximum byte count is 255 (0xFF). 16 (0x10) and 32 (0x20) are commonly used byte counts.

Should be able to choose variable byte_count ranging from 1 to 255 when writing the hex file.

[wexi]

It's indeed a useful feature. To increase Flash uploading speed I made the following simple patch:
diff.txt
May I suggest incorporating this, raising an exception perhaps if the new data_rec_len is outside range.

Thanks, Enoch.

[Martoni]

@wexi, Your patch works for me.

[bialix]

@erki1993 Thanks, your patch is merged now.