Feature to format floating point numbers

[Vanmaele]

This work allows to format floating point, either set the decimal point or significant number. If not format preference are given then the driver behaves as before.

Note that JSON specifies to print numbers in it's shortest form, this is still the case e.g. but a number will not be printed longer than e.g. a given decimal point. But a number that has been formatted with a decimal point won't be printed in a scientific notation.

[Tvalley71]

The length needs to be adjusted if trailing zeros are removed or else a 0-termination is copied into the output buffer.

    else if (item->type & cJSON_NumberIsFormatted)
    {
        precision = _get_precision_from_item(item, sizeof(number_buffer));
        if (item->type & cJSON_NumberFormatStyleFixedPoint)
        {
            sprintf((char*)number_buffer, "%.*f", (int)precision, d);
            remove_trailing_zeros((char*)number_buffer);
            length = strlen((char*)number_buffer); /*     <================    */
        }
        else
        {
            length = sprintf((char*)number_buffer, "%.*g", (int)precision, d);
        }
    }