return type is not strictly assumed to be boolean; it now
returns a :class:`.Boolean` subclass called :class:`.MatchType`.
The type will still produce boolean behavior when used in Python
expressions, however the dialect can override its behavior at
result time.  In the case of MySQL, while the MATCH operator
is typically used in a boolean context within an expression,
if one actually queries for the value of a match expression, a
floating point value is returned; this value is not compatible
with SQLAlchemy's C-based boolean processor, so MySQL's result-set
behavior now follows that of the :class:`.Float` type.
A new operator object ``notmatch_op`` is also added to better allow
dialects to define the negation of a match operation.
fixes #3263

sqlalchemy/orm, sqlalchemy/event, sqlalchemy/testing

to get all flake8 passing

implements PG's to_tsquery('regconfig', 'arg') pattern. fixes #3078

:meth:`.Operators.__or__` and :meth:`.Operators.__invert__`
operator overload methods could not be overridden within a custom
:class:`.TypeEngine.Comparator` implementation.
fixes #3012

renders "BETWEEN SYMMETRIC".  Also added a new negation operator
"notbetween_op", which now allows an expression like ``~col.between(x, y)``
to render as "col NOT BETWEEN x AND y", rather than a parentheiszed NOT
string.  fixes #2990

erroneously passed a column expression whose comparator included
the ``__getitem__()`` method, such as a column that uses the
:class:`.postgresql.ARRAY` type. [ticket:2957]

with conjunctions, e.g.
``None`` :func:`.expression.null` :func:`.expression.true`
:func:`.expression.false`, including consistency in rendering NULL
in conjunctions, "short-circuiting" of :func:`.and_` and :func:`.or_`
expressions which contain boolean constants, and rendering of
boolean constants and expressions as compared to "1" or "0" for backends
that don't feature ``true``/``false`` constants. [ticket:2804]

specified) is now copied when used in a typed expression, and the
new copy is assigned the actual type of the compared column.  Previously,
this logic would occur on the given :func:`.bindparam` in place.
Additionally, a similar process now occurs for :func:`.bindparam` constructs
passed to :meth:`.ValuesBase.values` for a :class:`.Insert` or
:class:`.Update` construct. [ticket:2850]