Mypy-boto3

Fixed
- `[types-aiobotocore]` Mark `boto3.dynamodb.table.BatchWriter` import as optional

Fixed
- `[aiobotocore-services]` Wrong indentation in `README.md` examples (reported by ytoku in 161)
- `[builder]` Python code blocks in MarkDown documents are formatted with `black`

Fixed
- `[boto3-stubs]` Added `boto3.s3.inject` module stubs
- `[boto3-stubs]` Allow `boto3.session.Session` usage (reported by sarisia in 160)

Fixed
- Allow `from boto3 import Session` (reported by kingakimbrel in 160)

Changed
- `[botocore-stubs]` Is no longer generated, moved to [botocore-stubs](https://github.com/youtype/botocore-stubs) repository

Fixed
- `[types-aiobotocore]` Invalid imports in `httpsession` module

Fixed
- `[boto3-stubs]` No longer provides a module interface
- `[botocore-stubs]` No longer provides a module interface
- `[lambda]` `InvocationResponseTypeDef` hack removed, now correctly parsed as a response structure (reported by mew1033 in 159)
- `[sqs]` `AttributeNames` argument in many methods accepted wrong values due to a bug in `botocore` (reported by ngnpope in 158)
- `[builder]` Generated `setup.py` files have proper docstrings