Number precision customization

[icasdri]

Allow users to configure/customize the desired precision of calculations and display.

We would like to expose the following under-the-hood math.js options in a nice configurable interface.

• math.config's number: toggle between "Number" and "BigNumber"
• math.config's precision: if using "BigNumber" limit max calculation precision
• math.format's notation, precision, and exponential: see http://mathjs.org/docs/reference/functions/format.html