Fix bug in linalg.diag
Merge pull request #70 from untom/fix_diag

Fix type bug and use CUBLAS in linalg.diag().
Don't set unicode_literals in scikits.cuda.utils; it breaks elftools.
Update CHANGES.
Update add_diag() tests to conform to default overwrite param.
Rename overwrite_a -> overwrite in inv().
Rewrite linalg.multiply() to use ElementwiseKernel.
Rewrite linalg.eye() to use ElementwiseKernel.
Use ElementwiseKernel to suppress small singular values in linalg.pinv().