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

N occurrences of a parameterized string.   This allows parameterized
warnings that can refer to their arguments to be delivered a fixed
number of times until allowing Python warning filters to squelch them,
and prevents memory from growing unbounded within Python's
warning registries.
fixes #3178

if we already have a table; this prevents reentrant calls and
we aren't supporting columns/etc being moved around between different parents

:class:`.SynonymProperty` and :class:`.ComparableProperty`.
- The ``info`` parameter has been added as a constructor argument
to all schema constructs including :class:`.MetaData`,
:class:`.Index`, :class:`.ForeignKey`, :class:`.ForeignKeyConstraint`,
:class:`.UniqueConstraint`, :class:`.PrimaryKeyConstraint`,
:class:`.CheckConstraint`.

fixes #2963

information regarding #3027.

sqlalchemy/orm, sqlalchemy/event, sqlalchemy/testing

to get all flake8 passing

fixes #3110