Render 64-bit integers as strings in JSON

When rendering a server-side object containing 64-bit integers, precision can be lost if it is rendered as a number. For example, if a JSON document contains the number 9219976635399687875, JavaScript will parse it as 9219976635399688000. This is caused by JavaScript only having floating point numbers. To ensure very large numbers are not rounded, render the value out as a string, e.g. "9219976635399687875".