Add DDL association to Table, CreateView support

Add DDL association to Table, CreateView support

Added support for the SQL ``CREATE VIEW`` statement via the new
:class:`.CreateView` DDL class. The new class allows creating database
views from SELECT statements, with support for options such as
``TEMPORARY``, ``IF NOT EXISTS``, and ``MATERIALIZED`` where supported by
the target database. Views defined with :class:`.CreateView` integrate with
:class:`.MetaData` for automated DDL generation and provide a
:class:`.Table` object for querying.

this alters the CreateTableAs commit:

* adds the ability for Table to be associated with Create and Drop
  DDL constructs
* Adds CreateView variant of CreateTableAs
* Both associate themselves with Table so they take place in
  create_all/create/drop_all/drop

Fixes: #181
Change-Id: If3e568d3d6a6ce19e3d15198c3fbbe06bd847c83