Andrey Zakharevich

``` julia> B = GBVector([3, 4, 5, 6, 7], [3, 4, 5, 6, 7]) 7x1 GraphBLAS int64_t matrix, bitmap by col 5 entries, memory: 272 bytes (3,1) 3 (4,1) 4...

This PR adds several features: 1. Migrate to OCaml 4.12.0, the main changes are caused by the fact that Core package developers removed polymorphic comparisons, so I've replaced them with...