jsbn-based arbitrary precision operations on currency amounts "XXX.YY"; because floats are BAD for representing money

Adds, multiplies the currency *amounts,* and calculates percentages of *amounts.* The result of
each of those operations is also an *amount:* a string, strictly matching the `/^\-?\d+\.\d\d$/`

pattern, like "0.25", "1000.00", or "-42.10".

*Amounts* on input and output are arbitrary large and precise:

```
99999999999999999999999999999999999999999999999999999999999999999999999999999999.99
+
0.01
=
100000000000000000000000000000000000000000000000000000000000000000000000000000000.00
```

However, in cases when the division is involved — like for percentage calculation — the result is rounded to the whole cent.

```
money.percent("0.50", "33.00") // is "0.17" instead of "0.165"
```

As a bonus feature, there's a simple formatting function for *amounts* in CHF, EUR, USD, GBP, and
JPY.

```
money.format("EUR", "-1560.00") // "-1.560,00"
```

Because storing currency amounts in floats is a really bad idea

Works both on Node and in the browser.

```
$ npm install --save money-math
```

Then

```
var money = require("money-math");
money.add("16.11", "17.07"); // "33.18"
money.subtract("16.00", "7.00"); // "9.00"
money.mul("24.00", "0.25"); // "6.00"
money.div("64.00", "2.00"); // "32.00"
money.percent("200.00", "3.25"); // "6.50"
money.format("JPY", "236800.00"); // "236,800"
money.floatToAmount(56.345); // "56.35"
```

And last, but not least :)

```
money.roundUpTo5Cents("42.02"); // "42.05"
money.roundTo5Cents("442.26"); // "442.25"
```

Which we use for bills in CHF that are required by law to be 0 (mod 5).

The *amount* strings are expected to strictly adhere to the format described by the regular
expression noted above. Thus, for example, it must be:

`"10.10"`

, not`"10.1"`

, not`"10.100"`

;`"10.00"`

, not`10`

, not`"10"`

, not`"10.0"`

.

That's a precondition for any of the API functions accepting *amount* arguments to work correctly. I
understand that it may be confusing to some of new users; but I believe that's an optimally
pragmatic way to mimic, by convention, an algebraic data type in idiomatic JavaScript -- a (very)
dynamically typed language.

Luckily, you can always move your arbitrary float value into the *amounts field* with
`money.floatToAmount(...)`

. Once all the values are *amounts,* money-math guarantees that all the
*field* operations keep the results withing the *field.* Classic algebra.