Unify PDMat and PDSparseMat + move SparseArrays support to an extension
#272
| Job | Run time |
|---|---|
| 1m 31s | |
| 1m 56s | |
| 1m 30s | |
| 1m 45s | |
| 3m 26s | |
| 3m 39s | |
| 2m 17s | |
| 2m 51s | |
| 3m 3s | |
| 3m 24s | |
| 3m 57s | |
| 29m 19s |