Marking internal interfaces as @api private.
Removed the Seahorse::VERSION constant.
Marked a few more internal interfaces as @api private.
Structure#to_h no longer expands StringIO objects.

Also made the default behavior of `#to_h` available as
`#orig_to_h`.
Added some docs to Aws::Structure.
Added unit tests for Aws::EmptyStructure.
Added unit tests for the null paging provider.
Added a plugin that simplifies working with DynamoDB attribute values.

This plugin changes the default format of request params and
response data that represents an Amazon DynamoDB attribute value.
Prior to this plugin, you would have to serialize request
parametes with their type, e.g.

    { s: 'string-value' }
    { n: "5.0" }

This plugin changes `Aws::DynamoDB::Client` operations to accept
and return simplified ruby-name values, such as:

    "string-value"
    5.0

This affects **every** DynamoDB request and response
structure that accepts or returns an attribute value.

This is a backwards-incompatible change. To revert to
the previous behavior, toggle simple attributes off:

    # disable this new default behavior
    Aws::DynamoDB::Client.new(simple_attributes: false)
Added upgrading notes to the README for the upcoming rc15.
Removed the static method from Aws::Api::Minifier.

Also removed un-exercised functionality from the API manifest.
Extracted API documenting logic into a class from the api YARD plugin.

Logic moved into `Aws::API::Documenter`.
Renamed operation documenting classes for clarity.
Updated doc plugin to consume API documentation from separate JSON files.
Separated documentation from the API models.

The primary reason to move the documentation from the API
JSON model files was to reduce the file of the published gem.
With this change, the gem file is reduced from ~740KB down
to ~280KB.

This change also has the benefit that API doc updates will not create
as much churn into the model files. Additionally, it will be easier
to audit what API params have no documentation.
Enabled coverage reports by default when running tests.