Autoboto

* Fixes detection of primitive types in Python 3.7
* Adds `typing_inspect` dependency which could simplify `type_info.py` a lot.
* Fixes tox pytest arguments for `pytest-random-order`
* Fixes test with the new union type hint for "enums"

* Remove paginate methods from OutputShapes which don't have pagination so that it doesn't appear in auto-complete.
* No more enum class because enum value lists in botocore are not complete and also when returning enum value, user wants the real value, not the enum item.
* Fixes nested dataclasses which have no value set.
* README updated

* Fixes enum serialisation and deserialisation - 16
* Adds `paginate()` method to the objects returned by operations which support pagination.

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- Sanity check the code in the build directories. And copy to target_dir only on success.

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- Extract autoboto generation code in a completely separate non-autoboto package.
- Use a dedicated directory for test builds.
- Simplify build directory structure -- do not write directly to `autoboto/services`. Instead write to a temporary space where all the dependencies are available.
- Switch to wr-profiles v4.0
- tox
- Stop using `typing.GenericMeta` which is not available in Python 3.7
- Add `boto_fields` and `autoboto_fields` descriptors on all shapes to simplify introspection for user.
- Expose `botocore_version` in the generated `autoboto` package. Expose as a tuple (major, minor, patch). There is no point in exposing boto3 version because it is not used in code generation.

- Add response_metadata to all shapes that are output shapes. All Client methods return a dictionary with `ResponseMetadata` even when they say they return nothing. So we must default to some base response shape (dataclass) which all response shapes inherit from and which has the `response_metadata` field. It is mandatory anyway.
- Add property to shapes that allow easy detection if they are strictly output shapes.
- Add property to shapes that allow easy detection if they are strictly input shapes.
- Replace `Style` with `BotogenConfig` which is backed by `BotogenEnv(Profile)`.
- Combine `generate` with `Botogen` — no need for this separation.
- Separate development requirements from install requirements - `html2text`, `pygments`, `yapf` and others are not needed for install.
- Execute all generated shapes modules.
- Allow passing botogen options via command-line. In particular, the services to generate, the build directory, target package. Allow disabling the formatter so that on the first run we just generate all and execute all without waiting for formatter. Allow passing flag to disable/enable execution of the generated module code.
- Make `Client` available at `autoboto.services.<service_name>.Client`
- Add string representation for `_NOT_SET` and make it falsey.
- Add a README.rst file under `autoboto/services` telling users and developers that python files in the directory are generated.