add canopy clustering application
Merge branch 'master' of github.com:spartan-array/spartan
add tile_operation and TileOpExpr into spartan.expr to support directly
return map result to master. This supports the operations in which we don't
know the shape of each map output.
remove unnecessary import from tile_opertion
Merge pull request #118 from MaggieQi/master

add canopy clustering application