- apply autopep8 + manual fixes to most of test/sql/

Found using: https://github.com/intgr/topy

more flexible ways to set up bound parameters and return types;
in particular, a :func:`.text` can now be turned into a full
FROM-object, embeddable in other statements as an alias or CTE
using the new method :meth:`.TextClause.columns`.
[ticket:2877]

- went through examples/ and cleaned out excess list() calls

for now
- fix up adaptation tests to still try to exercise the correlation argument

so it can be managed more easily

- update "not supported" messages for empty inserts, mutlivalue inserts

- rework the ValuesBase approach for multiple value sets so that stmt.parameters
does store a list for multiple values; the _has_multiple_parameters flag now indicates
which of the two modes the statement is within.  it now raises exceptions if a subsequent
call to values() attempts to call a ValuesBase with one mode in the style of the other
mode; that is, you can't switch a single- or multi- valued ValuesBase to the other mode,
and also if a multiple value is passed simultaneously with a kwargs set.
Added tests for these error conditions

- Calling values() multiple times in multivalue mode now extends the parameter list to
include the new parameter sets.

- add error/test if multiple *args were passed to ValuesBase.values()

- rework the compiler approach for multivalue inserts, back to where
_get_colparams() returns the same list of (column, value) as before, thereby
maintaining the identical number of append() and other calls when multivalue
is not enabled.  In the case of multivalue, it makes a last-minute switch to return
a list of lists instead of the single list.  As it constructs the additional lists, the inline
defaults and other calculated default parameters of the first parameter
set are copied into the newly generated lists so that these features continue
to function for a multivalue insert.   Multivalue inserts now add no additional
function calls to the compilation for regular insert constructs.

- parameter lists for multivalue inserts now includes an integer index for all
parameter sets.

- add detailed documentation for ValuesBase.values(), including careful wording
to describe the difference between multiple values and an executemany() call.

- add a test for multivalue insert + returning - it works !

- remove the very old/never used "postgresql_returning"/"firebird_returning" flags.

cutting up tests and removing old ones
- move test_in() to test_operators
- slice up migrated operator tests into TOT

      by proxy that of :class:`.orm.Query`, will not
      take effect for a SELECT statement that is being
      rendered directly in the FROM list of the enclosing
      SELECT.  Correlation in SQL only applies to column
      expressions such as those in the WHERE, ORDER BY,
      columns clause. [ticket:2595]