Build Plate Library v2

This is an updated version of Makerbot's "Build Plate Library for Customizer". I updated the library to include as many new printers as I could easily find data for.

**Usage**

1. Include TNH_build_plate.scad in your scad document
2. Call build_plate(); with your printer selected as the first argument.

For example: `build_plate(20);` will display a build plate for the "Makerbot Replicator 2X"

You can manually specify your build plate dimensions using the second and third arguments.