Unify PDMat and PDSparseMat + move SparseArrays support to an extension
#273
| Job | Run time |
|---|---|
| 2m 54s | |
| 3m 27s | |
| 2m 22s | |
| 2m 53s | |
| 3m 15s | |
| 3m 38s | |
| 2m 17s | |
| 2m 43s | |
| 2m 39s | |
| 3m 26s | |
| 4m 3s | |
| 33m 37s |