Add ability to add zeroes after digits in fraction

[asvishnyakov]

In gitter client says:

public class MathFilters
{
    public static object Round(object input, int digits = 0)
    {
        if (input != null)
        {
            input = Math.Round(Convert.ToDecimal(input, CultureInfo.InvariantCulture), digits);
        }
        return input;
    }

I modified this method because the Round method was always returning a value with only 1 number after the decimal Convert.ToDouble(input) was returning for example 100.1 and the Math.Round method was then never returning a 100.10 value is in the Liquid template I have round: 2 {{ value | round: 2 }}

Do not use this code, because you will loose a part of fraction. Instead, add options for round or create new tag.

[tatarincev]

Need to add new liquid filter format similar as is made there https://github.com/dotliquid/dotliquid/issues/111

[asvishnyakov]

Filter works as expected:

{% assign test = 11.22 %}
{{ test | format: '#0.000' }}
output: 11.220
{% assign test = 11.22 %}
{{ test | format: 'e3' }}
output: 1.122E+001

(syntax is the same as for Int32.ToString), but it's not applicable to prices, because they renders on client side through angular. Standard angular number filter with may be used instead to specify fraction size.