Mod10 Function

The parameters for the MOD10 function are as follows:
Dir 0 = start on right
Dir 1 = start on left

```Direction = 0 (right to left)
1   2   1   2   1   2   1   2   1   2   1   2   1   2   1   2   1   2   1   2   1   2   1   2   1   2   1   2   1   2
End here     ← ← ← ←     ← ← ← ←     ← ← ← ←    Go this direction     ← ← ← ←     ← ← ← ←      ← ← ← ←     Start here

Direction = 0 (right to left)
2   1   2   1   2   1   2   1   2   1   2   1   2   1   2   1   2   1   2   1   2   1   2   1   2   1   2   1   2   1
End here     ← ← ← ←     ← ← ← ←     ← ← ← ←    Go this direction     ← ← ← ←     ← ← ← ←      ← ← ← ←     Start here

Direction = 1 (left to right)
2   1   2   1   2   1   2   1   2   1   2   1   2   1   2   1   2   1   2   1   2   1   2   1   2   1   2   1   2   1
Start here     → → → →     → → → →     → → → →    Go this direction     → → → →     → → → →     → → → →      End here

Direction = 1 (left to right)
1   2   1   2   1   2   1   2   1   2   1   2   1   2   1   2   1   2   1   2   1   2   1   2   1   2   1   2   1   2
Start here     → → → →     → → → →     → → → →    Go this direction     → → → →     → → → →     → → → →      End here```

Ucompose uses the Luhn algorithm to calculate the check digit.
http://en.wikipedia.org/wiki/Luhn_algorithm

The following example assumes a weight of 0 and a direction of 0.
(2,1,2,1,... starting from the right)

```Account number      0  0  4  1  7  8  0  0  0  0  0  0  0  0  0  1  3  0  3  7  x
Weight              1  2  1  2  1  2  1  2  1  2  1  2  1  2  1  2  1  2  1  2  x
Multiply by weight  0  0  4  2  7  16 0  0  0  0  0  0  0  0  0  2  3  0  3  14 x
Sum of digits       0  0  4  2  7  7  0  0  0  0  0  0  0  0  0  2  3  0  3  5  = 33
MOD10 check digit                                                               = 7

The check digit (x) is obtained by computing the sum of digits then computing 9 times that value modulo 10.

In equation form:
(33 * 9) mod 10

In algorithm form:
Compute the sum of the digits (33).
Multiply by 9 (297).
The last digit, 7, is the check digit.
```