BREAKING CHANGE:

* **core:** `stack.name` renamed to `stack.stackName`
* **core:** `stack.stackName` will return the concrete stack name. Use `Aws.stackName` to indicate { Ref: "AWS::StackName" }.
* **core:** `stack.account` and `stack.region` will return the concrete account/region only if they are explicitly specified when the stack is defined (under the `env` prop). Otherwise, they will return a token that resolves to the AWS::AccountId and AWS::Region intrinsic references. Use `Context.getDefaultAccount()` and `Context.getDefaultRegion()` to obtain the defaults passed through the toolkit in case those are needed. Use `Token.isUnresolved(v)` to check if you have a concrete or intrinsic.
* **core:** `stack.logicalId` has been removed. Use `stack.getLogicalId()`
* **core:** `stack.env` has been removed, use `stack.account`, `stack.region` and `stack.environment` instead
* **core:** `stack.accountId` renamed to `stack.account` (to allow treating account more abstractly)
* **core:** `AvailabilityZoneProvider` can now be accessed through `Context.getAvailabilityZones()`
* **core:** `SSMParameterProvider` can now be accessed through `Context.getSsmParameter()`
* **core:** `parseArn` is now `Arn.parse`
* **core:** `arnFromComponents` is now `arn.format`
* **core:** `node.lock` and `node.unlock` are now private
* **core:** `stack.requireRegion` and `requireAccountId` have been removed. Use `Token.unresolved(stack.region)` instead
* **core:** `stack.parentApp` have been removed. Use `App.isApp(stack.node.root)` instead.
* **core:** `stack.missingContext` is now private
* **core:** `stack.renameLogical` have been renamed to `stack.renameLogicalId`
* **core:** `IAddressingScheme`, `HashedAddressingScheme` and `LogicalIDs` are now internal. Override `Stack.allocateLogicalId` to customize how logical IDs are allocated to resources.