v3.0.0

Improved modularization

It should now be an easy process to add new styles/platforms.

Level 0: 
- DiffableTextKit

Level 1:
- DiffableTextViewsXiOS

Level 2: 
- DiffableTextStylesXNumeric
- DiffableTextStylesXPattern
- DiffableTextStylesXWrapper

Level 3:
- DiffableTextStyles [exports Level 2]

Level 4:
- DiffableTextViews  [exports Level 1 & 3].

Import reduced to a single statement

Because the project has been restructured, it is now sufficient to import DiffableTextViews.

Fixes and improvements

#57. NSCache did not return a value for custom keys, so new values were created (and cached up to the cache's size limit) on each view update. This has been fixed, so this update should include a performance boost.