Recognize item boundaries when creating diff strings

As discussed on the ticket https://github.com/google/truth/issues/239,

Currently a diff would print as (in this case bytes are coded to hex)
`Not true that <(byte[]) [0, 1]> is equal to <[1, 0]>; expected:<0[100]> but was:<0[001]>`

But the resulting output is not very clean since the diff window do not follow **or know** the rule about 2 chars for a byte in hex. This may apply in other cases of array comparisons. (I haven't tested the scenario)
Array 1 : 1112, 2223, 3333
Array 2 : 1111, 3456, 6333
Will/May create a diff like `<111[2, 2223, 3]333> but was <111[1, 3456, 6]333>`