Unify PDMat and PDSparseMat + move SparseArrays support to an extension
#236
| Job | Run time |
|---|---|
| 2m 33s | |
| 2m 54s | |
| 2m 3s | |
| 2m 32s | |
| 2m 29s | |
| 3m 2s | |
| 3m 58s | |
| 4m 41s | |
| 6m 13s | |
| 2m 58s | |
| 3m 39s | |
| 37m 2s |