Fix `SQLAlchemy.destroy`: `open()` does not return an SQLAlchemy engine object

[amotl]

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Dear Mark,

thanks a stack for conceiving this excellent package.

While working on GH-106, we discovered a minor flaw in the SQLAlchemy.destroy method. This patch fixes it. Along the lines, it slightly adjusts the .gitignore file, and the pytest configuration options.

With kind regards, Andreas.