This completes w1-eeproom.c with the complete API. The provided test
commands allow to read and write any size at any offset (the low-level
code manages cross-page reads and writes. The following examples
modify a pre-written eeprom, which I host in an external socket of
my SPEC card:

   wrc# w1r 0 4
   read(0x0, 4): result = 4
   offset    0 (0x000): 240 (0xf0)
   offset    1 (0x001): 241 (0xf1)
   offset    2 (0x002): 242 (0xf2)
   offset    3 (0x003): 243 (0xf3)

   wrc# w1w 0 40 41 42
   offset    0 (0x000):  40 (0x28)
   offset    1 (0x001):  41 (0x29)
   offset    2 (0x002):  42 (0x2a)
   write(0x0, 3): result = 3

   wrc# w1r 0 4
   read(0x0, 4): result = 4
   offset    0 (0x000):  40 (0x28)
   offset    1 (0x001):  41 (0x29)
   offset    2 (0x002):  42 (0x2a)
   offset    3 (0x003): 243 (0xf3)

   wrc# w1r 30 4
   read(0x1e, 4): result = 4
   offset   30 (0x01e):  69 (0x45)
   offset   31 (0x01f):  70 (0x46)
   offset   32 (0x020):  71 (0x47)
   offset   33 (0x021):  72 (0x48)

   wrc# w1w 30 11 22 33 44 55 66
   offset   30 (0x01e):  11 (0x0b)
   offset   31 (0x01f):  22 (0x16)
   offset   32 (0x020):  33 (0x21)
   offset   33 (0x021):  44 (0x2c)
   offset   34 (0x022):  55 (0x37)
   offset   35 (0x023):  66 (0x42)
   write(0x1e, 6): result = 6

   wrc# w1r 30 6
   read(0x1e, 6): result = 6
   offset   30 (0x01e):  11 (0x0b)
   offset   31 (0x01f):  22 (0x16)
   offset   32 (0x020):  33 (0x21)
   offset   33 (0x021):  44 (0x2c)
   offset   34 (0x022):  55 (0x37)
   offset   35 (0x023):  66 (0x42)
Signed-off-by: Alessandro Rubini <rubini@gnudd.com>