add cholesky matrix decomposition
rename disdca_svm
reduce the map operations in each iteration in cholesky
rename SealArray to SealedArray
remove with_array and with_ex parameters from fn_kw of region_map
change comments of fn parameter in region_map
Merge pull request #101 from MaggieQi/cholesky

Add disdca_svm and cholesky into examples
Merge branch 'master' of github.com:spartan-array/spartan

Conflicts:
	spartan/examples/cholesky.py
	spartan/expr/region_map.py
	tests/test_cholesky.py