ReadOnlySequence version

[benaadams]

Using PR dotnet/corefx#27499

                                     Method |       Mean | Scaled |
------------------------------------------- |-----------:|-------:|
     'Only generate the random item index.' |   1.732 ns |   0.01 |
...y static data to the stack using Spans.' |  27.461 ns |   0.19 |
...e stack using a locally generated Span.' | 147.255 ns |   1.00 |
... implemented SafeBufferSlice<T> struct.' | 152.654 ns |   1.04 |
...k using the ReadOnlySequence<T> struct.' | 214.572 ns |   1.46 |

[hexawyz]

Woah, thanks a lot for this quite massive upgrade 😮
I expected to have to wait for the new packages to come out, but it seems I don't have to 😉