Auto-create category for features

[nerdsRob]

Add a binary with usageflip-the-switch category.

This call auto-generates a FlipTheSwitch+Features.{h,m} files for enabled/disabled features such as:

/* AUTO-GENERATED. DO NOT ALTER */

@interface FlipTheSwitch (Features)
+ (BOOL)isAmazingThingEnabled;
+ (void)enableAmazingThing;
+ (void)disableAmazingThing;
+ (void)setAmazingThingEnabled:(BOOL)enabled;
@end

By default, this should read a yaml file (if exists) at the current location, and generate the FlipTheSwitch+Features.{h,m} files from it.
Extra options are:

• input specifies the location directory of the features.yml file to read
• output specifies the location directory of the FlipTheSwitch+Features.{h,m} files to create
• enabled specifies extra features to be set as enabled
• disabled specifies extra features to be set as disabled