Release 2.0.0

V2 was merged in #892, which included the work of all of these contributors: @asahasrabuddhe, @meatballhat, @jszwedko, @lynncyrin, @AudriusButkevicius, @saschagrunert, @rliebz, @johnweldon, @nlewo, @grubernaut, @OneOfOne, @VMitov, @cbranch, @marwan-at-work, @uudashr, @bfreis

Discuss the state of V2 here => #826

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Added

• Added NewStringSlice and NewIntSlice for creating their related types
• Added Float64SliceFlag for unmarshaling a list of floats from the user
• Added Context.Lineage to get all contexts from current up to global
• Added Context.LocalFlagNames to get the flag names from only the current context
• Added BoolFlag.Value to handle both default-false and default-true
• Added IsSet method to the Flag interface which allows us to detect whether or not a flag has been set

Changed

• Occurrences of []Command have been changed to []*Command
• Occurrences of []cli.Flag have been changed to []*cli.Flag
• Context.FlagNames now returns all flags in the context lineage
• Context.IsSet now considers the full context lineage

Removed

• Removed Global* flags since all flags are now global
  • when updating, replace GlobalBool with Bool
  • and GlobalInt with Int
  • and GlobalString with String
  • and so on for any other global flags
• Removed Context.Parent method, as this is now available via Context.Lineage
  • when updating, replace Context.Parent() with Context.Lineage()[1]
• Removed the App.Author and App.Email
  • these have been replaced with the Authors []*Author field
• Removed the ability to specify multiple entries in the Command.Name field
  • when updating, replace Name: "a, b, c" with Name: "a", Aliases: []string{"b", "c"}
• Removed the Command.ShortName field
  • when updating, replace ShortName: "i" with Aliases: []string{"i"}
• Removed all Context.Global* methods, as the non-global versions now traverse up
  the context lineage automatically.
• Removed the ability to specify &StringSlice{...string} or &IntSlice{...int}.
• Removed adapter code for deprecated Action func signature
• Removed BoolTFlag and related code, as this is now available via BoolFlag.Value