Refactor

This release includes following refactor result:

AngularLayer (a.k.a KnobLayer in previous version)

1. rename
2. remove addLayer(:), use SequenceBuilder instead of.
   1. SequenceBuilder has limitation of numbers. It allows most 10 layers.
   2. Support for-loop and if-else condition for create layers.
3. Implement property wrapper Clamping to limit max/min degrees to make code clear.

GradientBuilder

Import GradientBuilder to make color setup easier. Also add gradient color support on layers.

RingText

Add WordsBuilder to provide flexibility on it.

SphericText

Now, it supports different writing direction.

Other refactors

1. Reorganize package structure. --> CommonExt --> Common
2. Re-declare struct which has no property, and might be singleton to enum.
3. Update and improve documents