Add Statically typed CloudFormation Templates

References:
  #401, #425

…for Empty Collections (aws#401)

### Services
* Synced the V2 SDK with latest AWS service API definitions.

### SDK Breaking changes
* This update includes breaking changes to how the DynamoDB AttributeValue (un)marshier handles empty collections.

### Deprecations
* `service/s3/s3crypto`: Deprecates the crypto client from the SDK ([aws#394](aws/aws-sdk-go-v2#394))
  * s3crypto client is now deprecated and may be removed from the future versions of the SDK.
* `aws`: Removes plugin credential provider ([aws#391](aws/aws-sdk-go-v2#391))
  * Removing plugin credential provider from the v2 SDK developer preview. This feature may be made available as a separate module.
* Removes support for deprecated Go versions ([aws#393](aws/aws-sdk-go-v2#393))
  * Removes support for Go version specific files from the SDK. Also removes irrelevant build tags, and updates the README.md file.
  * Raises the minimum supported version to Go 1.11 for the SDK. Older versions may work, but are not actively supported

### SDK Features
* `service/s3/s3manager`: Add Upload Buffer Provider ([aws#404](aws/aws-sdk-go-v2#404))
  * Adds a new `BufferProvider` member for specifying how part data can be buffered in memory.
  * Windows platforms will now default to buffering 1MB per part to reduce contention when uploading files.
  * Non-Windows platforms will continue to employ a non-buffering behavior.
* `service/s3/s3manager`: Add Download Buffer Provider ([aws#404](aws/aws-sdk-go-v2#404))
  * Adds a new `BufferProvider` member for specifying how part data can be buffered in memory when copying from the http response body.
  * Windows platforms will now default to buffering 1MB per part to reduce contention when downloading files.
  * Non-Windows platforms will continue to employ a non-buffering behavior.
* `service/dynamodb/dynamodbattribute`: New Encoder and Decoder Behavior for Empty Collections ([aws#401](aws/aws-sdk-go-v2#401))
  * The `Encoder` and `Decoder` types have been enhanced to support the marshaling of empty structures, maps, and slices to and from their respective DynamoDB AttributeValues.
  * This change incorporates the behavior changes introduced via a marshal option in V1 ([aws#2834](aws#2834))

### SDK Enhancements
* `internal/awsutil`: Add suppressing logging sensitive API parameters ([aws#398](aws/aws-sdk-go-v2#398))
  * Adds suppressing logging sensitive API parameters marked with the `sensitive` trait. This prevents the API type's `String` method returning a string representation of the API type with sensitive fields printed such as keys and passwords.
  * Related to [aws#2310](aws#2310)
  * Fixes [aws#251](aws/aws-sdk-go-v2#251)
* `aws/request` : Retryer is now a named field on Request. ([aws#393](aws/aws-sdk-go-v2#393))
* `service/s3/s3manager`: Adds `sync.Pool` to allow reuse of part buffers for streaming payloads ([aws#404](aws/aws-sdk-go-v2#404))
  * Fixes [aws#402](aws/aws-sdk-go-v2#402)
  * Uses the new behavior introduced in V1 [aws#2863](aws#2863) which allows the reuse of the sync.Pool across multiple Upload request that match part sizes.

### SDK Bugs
* `service/s3/s3manager`: Fix index out of range when a streaming reader returns -1 ([aws#378](aws/aws-sdk-go-v2#378))
  * Fixes the S3 Upload Manager's handling of an unbounded streaming reader that returns negative bytes read.
* `internal/ini`: Fix ini parser to handle empty values [aws#406](aws/aws-sdk-go-v2#406)
  * Fixes incorrect modifications to the previous token value of the skipper. Adds checks for cases where a skipped statement should be marked as complete and not be ignored.
  * Adds tests for nested and empty field value parsing, along with tests suggested in [aws#2801](aws#2801)