Skytools

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Fixes:

* dbservice: py3 fix for row.values()
* skylog: Use logging.setLogRecordFactory for adding extra fields
* fileutil,sockutil: fixes for win32.
* natsort: py3 fix, improve rules.

Cleanups:

* Set up Github Actions for CI and release.
* Use "with" for opening files.
* Drop py2 syntax.
* Code reformat.
* Convert nose+doctests to pytest.

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* Support Postgres 10 sequences
* Make full_copy text-based
* Allow None fields in magic_insert
* Fix iterator use in magic insert
* Fix Python3 bugs
* Switch off Python2 tests, to avoid wasting time.

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* Separate 'skytools' module out from big package
* Python 3 support

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See old changes here:
https://github.com/pgq/skytools-legacy/blob/master/NEWS