Added compiler-level flags used by Postgresql to place additional
parenthesis than would normally be generated by precedence rules
around operations involving JSON, HSTORE indexing operators as well as
within their operands since it has been observed that Postgresql's
precedence rules for at least the HSTORE indexing operator is not
consistent between 9.4 and 9.5.

Fixes: #3806
Change-Id: I5899677b330595264543b055abd54f3c76bfabf2

The "eq" and "ne" operators are no longer part of the list of
"associative" operators, while they remain considered to be
"commutative".  This allows an expression like ``(x == y) == z``
to be maintained at the SQL level with parenthesis.  Pull request
courtesy John Passaro.

Fixes: #3799
Change-Id: I3759d8987b35649d7418b6524316c9e70c857e68
Pull-request: https://github.com/zzzeek/sqlalchemy/pull/308

Fixed issue in SQL math negation operator where the type of the
expression would no longer be the numeric type of the original.
This would cause issues where the type determined result set
behaviors.

Change-Id: If0e339614a3686e251235fc94b6f59310c4630a5
Fixes: #3735

None / True / False render as literals.
For SQLite, "IS" is used as SQLite lacks
"IS DISTINCT FROM" but its "IS" operator acts
this way for NULL.

Doctext-author: Mike Bayer <mike_mp@zzzcomputing.com>
Change-Id: I9227b81f7207b42627a0349d14d40b46aa756cce
Pull-request: https://github.com/zzzeek/sqlalchemy/pull/248

override with a column expression (e.g. by using ``'x' in col``)
would cause an endless loop in the case of an ARRAY type, as Python
defers this to ``__getitem__`` access which never raises for this
type.  Overall, all use of ``__contains__`` now raises
NotImplementedError.
fixes #3642

persistence of JSON values in MySQL as well as basic operator support
of "getitem" and "getpath", making use of the ``JSON_EXTRACT``
function in order to refer to individual paths in a JSON structure.
fixes #3547
- Added a new type to core :class:`.types.JSON`.  This is the
base of the PostgreSQL :class:`.postgresql.JSON` type as well as that
of the new :class:`.mysql.JSON` type, so that a PG/MySQL-agnostic
JSON column may be used.  The type features basic index and path
searching support.
fixes #3619
- reorganization of migration docs etc. to try to refer both to
the fixes to JSON that helps Postgresql while at the same time
indicating these are new features of the new base JSON type.
- a rework of the Array/Indexable system some more, moving things
that are specific to Array out of Indexable.
- new operators for JSON indexing added to core so that these can
be compiled by the PG and MySQL dialects individually
- rename sqltypes.Array to sqltypes.ARRAY - as there is no generic
Array implementation, this is an uppercase type for now, consistent
with the new sqltypes.JSON type that is also not a generic implementation.
There may need to be some convention change to handle the case of
datatypes that aren't generic, rely upon DB-native implementations,
but aren't necessarily all named the same thing.

- any/all work for Array as well as subqueries, accepted by MySQL
- Postgresql ARRAY now subclasses Array
- fixes #3516

"super" instead of hardcoding to "self.type" for the default return
value, the base Comparator was returning other_comparator.type.   It's
not clear what the rationale for this was, though in theory the
base Comparator should possibly even throw an exception if the two
types aren't the same (or of the same affinity?) .
- mysql.SET was broken on this because the bitwise version adds "0"
to the value to force an integer within column_expression, we are doing type_coerces here
now in any case so that there is no type ambiguity for this
operation

- The "hashable" flag on special datatypes such as :class:`.postgresql.ARRAY`,
:class:`.postgresql.JSON` and :class:`.postgresql.HSTORE` is now
set to False, which allows these types to be fetchable in ORM
queries that include entities within the row.  fixes #3499
- The Postgresql :class:`.postgresql.ARRAY` type now supports multidimensional
indexed access, e.g. expressions such as ``somecol[5][6]`` without
any need for explicit casts or type coercions, provided
that the :paramref:`.postgresql.ARRAY.dimensions` parameter is set to the
desired number of dimensions. fixes #3487
- The return type for the :class:`.postgresql.JSON` and :class:`.postgresql.JSONB`
when using indexed access has been fixed to work like Postgresql itself,
and returns an expression that itself is of type :class:`.postgresql.JSON`
or :class:`.postgresql.JSONB`.  Previously, the accessor would return
:class:`.NullType` which disallowed subsequent JSON-like operators to be
used. part of fixes #3503
- The :class:`.postgresql.JSON`, :class:`.postgresql.JSONB` and
:class:`.postgresql.HSTORE` datatypes now allow full control over the
return type from an indexed textual access operation, either ``column[someindex].astext``
for a JSON type or ``column[someindex]`` for an HSTORE type,
via the :paramref:`.postgresql.JSON.astext_type` and
:paramref:`.postgresql.HSTORE.text_type` parameters. also part of fixes #3503
- The :attr:`.postgresql.JSON.Comparator.astext` modifier no longer
calls upon :meth:`.ColumnElement.cast` implicitly, as PG's JSON/JSONB
types allow cross-casting between each other as well.  Code that
makes use of :meth:`.ColumnElement.cast` on JSON indexed access,
e.g. ``col[someindex].cast(Integer)``, will need to be changed
to call :attr:`.postgresql.JSON.Comparator.astext` explicitly.  This is
part of the refactor in references #3503 for consistency in operator
use.

in conjunction with :func:`.and_` or :func:`.or_` would fail
with an AttributeError.
fixes #3490