1.0-beta4

Welcome to the redux-undo team, @pl12133 and @tiemevanveen - and thanks for all contributions!

• remove redundant dependencies
• implement CLEAR_HISTORY action (thanks @pl12133)
• add gitter link to README.md
• more tests and some fixes (thanks to @pl12133 and @tiemevanveen)
• allow initialization of state from redux createStore (thanks to @tiemevanveen)
• clarify debug messages (thanks to @pl12133)
• make beta default (in README.md), add link to 0.6 README

Full list of changes/commits