zundo 0.2.0

add redo

on Node.js NPM

add redo function and add safety when applying previous and future states

• Merge pull request #3 from charkour/redo c93453c
• update docs 21901c3
• check for existing states before trying to undo/redo 3562e00
• add redo feature 1c61e1f
• Update README.md af2366d
• Update README.md 9bd237e
• Update README.md 88f32f6

v0.1.3...v0.2.0