Support decimal places

[neoecos]

@spookylukey I added decimal_placesto the Currency class, with the intention to use the currency decimal places as default parameter in the formatting.

Also added the decimal places to all currencies supported, and corresponding tests.

[spookylukey]

@neoecos - thanks so much for this patch and the effort you have put into it.

Unfortunately, we already made a decision that all formatting of currencies is now going to go through Babel - we are waiting for a patch for this - #22 (comment)

With that patch in place, this patch would become redundant - format.numbers.format_currency already has knowledge of decimal places built in:

>>> format_currency(1, 'USD')
'US$1.00'

>>> format_currency(1, 'BHD')
'BHD1.000'

and it has support for more customization with other options - http://babel.pocoo.org/en/latest/api/numbers.html#babel.numbers.format_currency

If you would like to have a go at implementing the patch as described in the other ticket, it would be very much appreciated! Sorry for wasted effort, but using Babel is going to give us many improvements long term.