Performance (heap reduction) for netcore and removal of regex

Performance (heap reduction) and removal of regex

• Heap-usage reduction in netstandard 2+ by switching key calls to span and altering array use in encoding.
• Removes regex dependency and changes hash parser to custom parser
• Addition of benchmarking projects
• Adds dependency on System.Memory for netstandard2.0|net452|net462|net472

Big thanks to Jos Vandertil (@jvandertil) for the help.