Add grant_view_privileges and revoke_view_privileges properly.

Previously, you could use grant_table_privileges and
revoke_table_privileges, but we may as well implement it for
completeness. (And because we did mention these methods in the
documentation.)
Add some tests for VIEWS.
Add some additional assertions for PostgreSQLExtensionAlterer.
Don't run tests on start up.
Remove unused exception class.
Add some documentation about ROLEs.
Fix variable name.
Improve test coverage.
Fix test name typos.
Leave the gem versioning to the Gemfile.
Ignore some vim files.
Simplify some feature checking code.
Add missing feature guard to test.
Fix up privileges test feature detection.
Add view options functionality.
Sort alphabetically.
Switch from Array() to Array.wrap.
Allow Strings or options Hashes for storage/index/etc. parameters.
Add support for materialized views.
Update the README with some new features.