Update of qr-method and addition of scan algorithm

qr-method: fixed tql2-algorithm for symmetric matrices
           added CUDA and OpenMP backends for symmetric matrices
           added tests and tutorials
           extracted tql2 algorithm

scan:      implemented inclusive and exclusive scan algorithms
           for CUDA, OpenCL and OpenMP backends
           developed tests
Merge pull request #100 from w2z43t5/master

Update of qr-method and addition of scan algorithm

qr-method: fixed tql2-algorithm for symmetric matrices
added CUDA and OpenMP backends for symmetric matrices
added tests and tutorials
extracted tql2 algorithm

scan: implemented inclusive and exclusive scan algorithms
for CUDA, OpenCL and OpenMP backends
developed tests