[currency] allow symbol to appear before negative sign / open paren

Currently, currency formatting puts the symbol before the "(" or "-" for negative numbers. This allows the user to put the symbol before the "(" or "-".

e.g. 
`numeral(-1000.238).format($(0,0.00)')` --> `$(1,000.24)`
`numeral(-1000.238).format($ -0,0')` --> `$ -1,000`