v1
Merge commit 'df047bc12d314d1ebb466eda0beac679d9f1de90' into refactor-api-action-handler
cell value helper
Merge commit '14a7430ae89717b03d93d2fa229b12cd1d5abfe9' into refactor-api-action-handler
chekc return if is a forumula
Merge commit '667d16ce34afec2cd36801cbb902c624e9e25863' into refactor-api-action-handler
refactor action handler, handling keystroke and other sepcial event from spreadsheet
some javadoc
Merge commit 'ff190413d46f29343fad12c5e1afcbed76f6c10f' into refactor-api-action-handler