3.0.0 Release

[nblumhardt]

• Optimized Parse.Sequence(...) combinator #94 - Parse.Sequence() (@nblumhardt)
• Fix the JSON parser sample to allow strings ending in '\'. #115 - JSON sample fix (@fvbommel)
• Update tooling; add a net5.0 target #122 - net5.0 target (@nblumhardt)
• Added OneOf combinator and tests #123 - Parse.OneOf() (@AndrewSav)
• Initial cut of <Nullable>enable</Nullable> #126 - nullable reference type annotations, AsNullable() combinator (@nblumhardt)
• Demo had typo in code #127 - sample fix (@Spaceman1861)
• Added Span.Until to Superpower.Parsers #129 - Span.Except() (@Ellested)
• Added optional error message to the Where combinator #131 - optional error message for Where() combinator (@AndrewSav)
• Add Matching method to Token class to support non-enum Tokens #132 - Token.Matching() (@AndrewSav)

[nblumhardt]

3.0.0-dev-00215 passes all of Seq's test suite :-) .. I think we're good to go!