What's new

Moved the documentation from the wiki into the repository so people can make pull requests.

System.CommandLine

Added support for setting environment variables using the [env:name=value] directive. (#965) Thanks, @fredrikhr!
Made constructors more consistent between Argument<T> and Option<T> to allow specifying getDefaultValue and description.
Added ParseResult.ValueForArgument<T>(Argument<T>) and ParseResult.ValueForOption<T>(Option<T>) to combine lookup and conversion into a single method supporting type inference. (#949)
Added default values to help output. (#898) Thanks, @NikiforovAll!
Help now wraps lines for long option names (#947) Thanks, @apogeeoak!
Added SymbolResult.FindResultFor to provide a cleaner way to find the result for a particular Command, Option, or Argument. This is similar to ParseResult.FindResultFor but it can be used within a custom parse delegate (ParseArgument<T>) so that you don't have to traverse the result tree.
Improved suggestion APIs to allow replacing the default suggestions, using Argument.Suggestions.Clear(). (#955) Thanks, @jmarolf!
Added Option.AddSuggestions and Argument.AddSuggestions methods with overloads to provide a static list of suggestions or a delegate for more dynamic suggestions.
Suggestions are now sorted so that the matches closest to what was typed are shown first. (#891) Thanks, @kimsey0!
Performance improvements in tokenizer and symbol result lookups.

Renamed Option.Required to Option.IsRequired.
Renamed the delegate type Suggest to SuggestDelegate.
Symbol.Aliases and Symbol.RawAliases are now of type IReadOnlyCollection<string> rather than IReadOnlyList<string>.