Allow all as required + improvements

• Can set each field as required
• Tag validate methods with discardable results
• Public error code enum to help error comparison

Minor improvements

• Remove JSON type alias
• fix double optional errors
• Like rule handling optional strings
• ignore Fastlane test outputs
• set common errors as public

Add Demo project

• A demo project using the development Pod was added.
• Livr was fixed to have some desired public interfaces (such as Validator and its usable methods)

Initial release

Releases LIVR validator for Swift.
Follows LIVR 2.0 spec