Extend support for conditionals

[svengiegerich]

For my project, I'm currently trying to use pytsql for use cases beyond replacing DB or table names. In particular, I want to make use of conditionals.
However, I run into some issues there:

• Executing certain functions within conditionals throws me (an) unexpected error(s)
  • E.g., if you want to parameterize whether a certain table or a view is created. For views, I use the following approach:

IF 1 = 1
BEGIN
     SET NONEXEC ON
END
GO
CREATE VIEW v AS ...
SET NONEXEC OFF

... however, pytsql indirectly throws me an unexpected error via sqlalchemy:
sqlalchemy.exec.ResourceClosedError: This result object does not return rows. It has been closed automatically. (If it's helpful I can also post the full error, but that requires some anonymization first)

• Declaring variables within the conditional seems current not possible.
  • while there is an obvious workaround by declaring every variable at the top of the file, pytsqls behavior is unexpected
  • I believe this is already addressed in issue SET statements for local variables are unreliable #19