Add nbody files
Refactor nbody and nbody benchmark.

Import spartan functions into global namespace, following conventions
from other examples.
Merge branch 'master' into add-nbody-simulations

Need diagonal function.
Initial swaption commit.
Finish changing nbody code for spartan

Add `set_diagonal` function.
Implement swaption example and add benchmark.

Swaption example still does not work because of slicing issues
(Expressions are read only).
Merge branch 'master' into add-nbody-simulations

Applies fix for travis status.
Add assign function.

assign(a, idx, value) returns a RegionMapExpr.
Merge branch 'assign' into 'swaption'
Fix spelling errors and Expr indexing
Add DistArray support to assign
Merge br 'assign' into 'swaption' for DistArray
Allow idx be TileExtent for assign; add more tests
Merge br 'assign' into 'swaption' for tile fix.
Merge br 'master' into 'swap' for ref count fix
Merge br 'assign' into swaption for mapper bug fix

Conflicts:
	spartan/expr/assign.py
	tests/test_assign.py
Fix swaption model
Fix assign
Add print statements
Merge pull request #177 from MaggieQi/master

change region_map to MapExpr so that it can be fusioned by optimization