to the aliasing syntax, as well as a new CTE feature
:meth:`.CTE.suffix_with`, which is useful for adding in special
Oracle-specific directives to the CTE.
fixes #3220

fixes #3036

method :meth:`.Query.with_statement_hint` to support statement-level
hints that are not specific to a table.
fixes #3206

on select().  improve some descriptions and add more info for limit()/
offset(), including new 1.0 functionality.

unify everything.
- create a new layer of separation between the "from order bys" and "column order bys",
so that an OVER doesn't ORDER BY a label in the same columns clause
- identify another issue with polymorphic for ref #3148, match on label
keys rather than the objects

- replace out _columns_clause_label with a straight boolean flag to
reduce the proliferation of labels

stringify a _label_reference() as is.
- add .key to _label_reference(), so that when _make_proxy()
is called, we don't call str() on it anyway.
- add a test to exercise Query's behavior of adding all the order_by
expressions to the columns list of the select, assert that things
work out when we have a _label_reference there, that it gets sucked
into the columns list and spit out on the other side, it's referred
to appropriately, etc.   _label_reference() could theoretically
be resolved at the point we iterate _raw_columns() but
it's better to just let things work as they already do (except
nicer, since we get "tablename.colname" instead of just "somename"
 in the columns list) so that we aren't adding a ton of overhead
to _columns_plus_names in the common case.

constructs are now importable from the "from sqlalchemy" namespace,
just like every other Core construct.
- The implicit conversion of strings to :func:`.text` constructs
when passed to most builder methods of :func:`.select` as
well as :class:`.Query` now emits a warning with just the
plain string sent.   The textual conversion still proceeds normally,
however.  The only method that accepts a string without a warning
are the "label reference" methods like order_by(), group_by();
these functions will now at compile time attempt to resolve a single
string argument to a column or label expression present in the
selectable; if none is located, the expression still renders, but
you get the warning again. The rationale here is that the implicit
conversion from string to text is more unexpected than not these days,
and it is better that the user send more direction to the Core / ORM
when passing a raw string as to what direction should be taken.
Core/ORM tutorials have been updated to go more in depth as to how text
is handled.
fixes #2992