Merge pull request #2 from sdalton1/master

Fixed Quick Start Guide link in README.md
Merge pull request #3 from sdalton1/master

Refactored smoothed aggregation preconditioner
Merge pull request #4 from sdalton1/master

Integrate multiple changes to multiplication and array2d access patterns
Silenced errors related to __host__ and __device__ tags in complex.h
Added several graph operations BFS, RCM, Hilbert space filling, etc. Depends on B40C.