* add root_line, root_column, and root_package_url to the json reporter

* update docs, pubspec, changelog

* enable the compact reporter and colors on windows, if stdout.supportsAnsiEscapes == true

* update pubspec/changelog, code review updates

We no longer support an SDK old enough that any of the referenced issues
are still a problem.

```
type 'WebSocketChannel' is not a subtype of type 'StreamChannel<String>' of 'channel'
```

Cast the `WebSocketChannel` to indicate that all values in each
direction will be `String`.

```
type 'CloseGuaranteeChannel<dynamic>' is not a subtype of type 'VirtualChannel'
```

Avoid using the `suiteChannel` variable for two types. It needs to start
as a `VirtualChannel` which has the `id` field, and then later be a
`StreamChannel`.

```
type 'RunnerSuite' is not a subtype of type 'FutureOr<Future<RunnerSuite>>'
```

Avoid the attempted Future flattening which was never correct but was
supported in the Dart 1 VM.

Fixes #840

Invoke a non-existing method after casting an object to `dynamic` to get
the behavior.

Prepare to release 0.12.38+1

- added `// ignore` comments for references to internal deprecated members
- removed comments referencing deprecated arguments
- upped args minimum constraint and migrated to `addMultiOption`
- dropped polymer support
- added `--fatal-infos` and `--fatal-warnings` to dartanalyzer test to prevent regressions and expose new warnings via cron jobs.
- fixed up some markdown issues

Closes #824

Makes test/frontend/never_called_test work with --preview-dart-2

Made members only used within a library private

There are no imports to this package.

- Delete dartium and content shell platforms
- Delete tests related to dartium
- Remove references to these platforms in docs
- Stop installing dartium on Travis

I'm not sure why the analyzer doesn't catch these, they appear to be
parse time bugs not runtime bugs when executing in the vm with
--preview-dart-2

Usage of 1.23 is non-existent
Increase turn-around on Travis

Fixes https://github.com/dart-lang/test/issues/800