Create test document for iPhone dimensions
Reorganize project to use includes

Managing the duplicate code from common.js has gotten cumbersome, so
it's time to start using #include. Continuing to support the
double-click installation method also makes it easier for a user to just
upgrade one plugin instead of both, which can lead to inconsistent
version issues.
Add support for iPhone display zoom mode

Add a checkbox to the plugin configuration dialog to enable simulation
of the iPhones 6 display zoom mode. This works by detecting either
320x568 or 375x667 artboards and adjusting the export size to generate a
preview at the appropriate size. Unfortunately the preview images end up
being slightly the wrong size, off by 2 and 1 pixels for the 6 and 6+
respectively.
Rename config plugin
Add dimensions to test artboards
Use strategies for scaling modes

Build out UI for new modes and move scaling code to common. Simulated
scaling for iPhones 6/6+ is off by 1-3 pixels in different scenarios.
Identify experimental modes
Update README for scaling modes
Reword explicit scaling option to be more HIGgy
Update CHANGELOG for release
Make scaling modes a subsection