Feature/allocate

`allocate` now supports the following form: `$m->allocate(1, 1, 1)` (array can be ommited)

Adds `allocateTo`: Divides the amount to N equal values (the remainder is shared between the first K results)

Example:
``` php
$m = new Money::EUR(15);

// Returns [8, 7]
$m->allocateTo(2);
```

Please merge #55 before, so I can rebase this if needed
I really dislike supporting two styles of methods. It creates confusion and bugs. Array is the best choice because it reflects the fact that it is a list of variable length.