Monotonic UlidRng no longer allows specifying the mask; we default to…

… masking out the MSB of the random part which gives us at least 2^79 bits before running into a sequenceoverflow. Also fixed a bug in the MonotonicUlidRng that caused an InvalidOperationException("Clock moved backwards; this is not supported.")

Merge branch 'master' of https://github.com/RobThree/NUlid

* Changed target frameworks to .Net 4.5 / NetStandard 2.0

* Got rid of magic number and moved it to const

* BenchmarkDotNet somehow breaks appveyor... will look into this later..

* Upped version to 1.1.

Merge branch 'master' of https://github.com/RobThree/NUlid.git