Pull args, intl, logging, shelf, and source_maps out of the SDK.

pkg/args/CHANGELOG.md

-## 0.12.2+1
-
-* Fix the built-in `help` command for `CommandRunner`.
-
-## 0.12.2
-
-* Add `CommandRunner` and `Command` classes which make it easy to build a
-  command-based command-line application.
-
-* Add an `ArgResults.arguments` field, which contains the original argument list.
-
-## 0.12.1
-
-* Replace `ArgParser.getUsage()` with `ArgParser.usage`, a getter.
-  `ArgParser.getUsage()` is now deprecated, to be removed in args version 1.0.0.
-
-## 0.12.0+2
-
-* Widen the version constraint on the `collection` package.
-
-## 0.12.0+1
-
-* Remove the documentation link from the pubspec so this is linked to
-  pub.dartlang.org by default.
-
-## 0.12.0
-
-* Removed public constructors for `ArgResults` and `Option`.
- 
-* `ArgResults.wasParsed()` can be used to determine if an option was actually
-  parsed or the default value is being returned.
-
-* Replaced `isFlag` and `allowMultiple` fields in the `Option` class with a
-  three-value `OptionType` enum.
-  
-* Options may define `valueHelp` which will then be shown in the usage.
-
-## 0.11.0
-
-* Move handling trailing options from `ArgParser.parse()` into `ArgParser`
-  itself. This lets subcommands have different behavior for how they handle
-  trailing options.
-
-## 0.10.0+2
-
-* Usage ignores hidden options when determining column widths.