Update README.md

typos
Update README.md
Start using polymer spark-menu-button
Made some delegate methods optional in TreeViewDelegate and ListViewDelegate. Fixed #402: Keep expanded/collapsed state of tree nodes.
remove Spark singleton
rename chrome_gen import prefixes to chrome
Merge pull request #430 from dart-lang/fix_polymer

remove Spark singleton
Merge pull request #377 from andersoyvind/master

Update README.md
Merge pull request #428 from dart-lang/new_menus

Start using polymer spark-menu-button
Small style fixes

https://github.com/dart-lang/spark/pull/424
Merge pull request #433 from ussuri/small-style-fixes

Small style fixes
Sorted files view (fixed #346). Select files properly after they're added to the workspace.
Merged
Simplified code
Merge pull request #429 from dinhviethoa/402-keep-expanded-state

Keep collapsed/expanded state of the files view
replace pub install to pub get
Merge pull request #432 from dart-lang/chrome_gen

rename chrome_gen import prefixes to chrome
Merged with upstream
Merge pull request #434 from dinhviethoa/346-sorted-files-view

Sorted files view.
Build version 0.0.20