Initial Commit
Add basic composition operators and helper functions

Based on work in https://github.com/objcio/issue-16-functional-apis
Add iOS Blur and most Color Adjustment filters
Create README.md
Complete implementation of CICategoryColorAdjustment filters
Add constructors for some CICategoryColorEffect filters

Progress on issue #1
Mark OSX-only filters as unavailable for iOS
Break filter categories into separate files.
Add all remaining CICategoryColorEffect category filters
Add CICategoryCompositeOperation filters
Refactor composite filters to a common foundation function
Add abstract filter generator for filters that take no arguments
Add some distortion filters
Add remaining distortion filters
Add CICategoryGenerator filters

Also renamed the singular filter generator.