Auto-create plist file for features

[michaelengland]

Add a binary with usageflip-the-switch plist.

This call auto-generates a Features.plist file for enabled/disabled features such as:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>amazing_thing</key>
    <true/>
</dict>
</plist>

By default, this should read a yaml file (if exists) at the current location, and generate a plist file from it.
Extra options are:

• input specifies the location directory of the features.yml file to read
• output specifies the location directory of the Features.plist file to create
• enabled specifies extra features to be set as enabled
• disabled specifies extra features to be set as disabled