Format money value as major units

[danielwitz]

I've added a functionality that allows the user to get the value of the money in major units (float64).
for example:

money.New(123456789, "EUR").AsMajorUnits() // 1234567.89

Also, I've filled out some more currencies and fixed some that we're incorrect like COP that supposed to have fraction of 2 but was set as 0.