Updated the build option.
Added discard-alpha option.
Version 2 implementation.

- Changed to work as an image effect.
- Added render mode option.
- Added gamma correction to preview display.
- Refactoring in several parts..
Improved stability.
Updated the document.
Update README.md
Added namespace definition.
Changed the default render mode.
Updated the unitypackage file.
Merge pull request #1 from keijiro/develop-ver2

Version 2