* Add from_file_parallel()
* Improve performance of operations on sparse arrays.
  - lil_matrix slicing is too slow. Use csr_matrix instead. Column
    slicing of csr_matrix is slower than row slicing, but it's still
    much faster than column slicing of lil_matrix.
  - csr_matrix can't support fancing indexing like csr[slicing] = update.
    Use hstack, vstack to implement to simulate fancing indexing. It's
    faster but can't support slicing with step is not 1. This should
    be enough for Spartan.
Add the missing csr_update
Comment and typo fixed.
Merge branch 'master' into from_file_parallel
Temporary version. But there is a memory leakage issue.
implement tile sharing for simple maps which use distarray _tile_mapper
add tile_sharing test
Merge branch 'master' of github.com:spartan-array/spartan

Conflicts:
	spartan/expr/transpose.py
Some optimization to speed up and reduce memory usage.
Merge branch 'master' into from_file_parallel

Conflicts:
	spartan/expr/write_array.py
Test refine
From file sparse version
Typo
Add accidently deleted files
Comment
add region_map which supports mapping over a region of an array. For
those tiles which are not in the region, reuse the tiles of the original
array.
Merge branch 'master' into from_file_parallel
Code refine
Merge branch 'optimization' into from_file_parallel

Conflicts:
	spartan/array/distarray.py
	spartan/expr/write_array.py
Remove redundant code