WS
Add ASTIndexBy
Add documentation for ASTIndexBy
Fix ASTIndexBy documentation
Merge branch 'master' into index-by
Add ASTIndexBy to Asterism.h and Readme
Implement ASTIndexBy using reduce
Fix function name in ASTIndexBy documentation
Return nil for nil collections in ASTIndexBy
Merge pull request #19 from robb/index-by

Add ASTIndexBy
Merge branch 'master' into group-by