- Fix syntax for upgrading errors in the analysis options
- Ignore todo hints since they are very noisy
- Enable check for implicit casts
- Fix a bunch of implicit casts in the test directory

More towards #842

- Export @Retry annotation (this is technically broken now but the corresponding tests only fail under preview-dart-2)
- Fix type issue with mapping over dynamic values

There are still errors in tests which may be harder to fix so we can't
check in the change to analysis options.

This should make it easier to diagnose Dart 2 semantic issues as more of
the places where there can be failures are explicit.

Most of the changes are just adding explicit `as` statements and keeping
the semantics that already existed. In a few places an uninitialized
`var` is given a type, and in others a reused variable name with
different types is split into multiple variables.

The changes in the frontend code are the most risky, since some users
might still be using that code in a non Dart 2 runtime and relying on
looseness which is lost with an explicit cast.

Pin to the dev.60 SDK for now since there are failures on the newer SDK.

The typedef was misused to mean either `Function` or `Function()` in
various places and worked because the difference was not checked. The
doc comment was also incorrect because there were places it was used
where a return value was explicitly necessary. Replace with an inline
function type definition using the appropriate choice for the location.

Where possible also replace with Function types that flow through the
required return types.

* 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