Add option to preserve trailing zeros in 'toDecimal' output

[austindd]

I would love to see an optional argument for toDecimal to preserve the exact number of digits specified in the digits argument by appending trailing zeros to the end of the output string. The current implementation will only enforce that the number of digits does not exceed the specified amount. Trailing zeros are essentially omitted.

This sort of thing probably doesn't matter when the result string is meant to be parsed back into a number. But it does occasionally matter for serialization and storage, especially when the exact level of precision must be known & enforced.