Latest stable release available from PyPi:
https://pypi.python.org/pypi/esptool/

This release:
https://pypi.python.org/pypi/esptool/1.3

New since v1.2.1:

• Python 2/3 support, esptool.py now works with Python 2.7+ or Python 3.4+
• esptool.py is now officially supported by Espressif Systems (software licensing & approach to development have not changed.)
• verify_flash command now accepts optional --flash_mode and --flash_speed arguments, allowing verification of a ROM bootable image at offset 0.
• Backport functional tests (test_esptool.py) from esptool v2.0

Thanks to @thespooler, @jeremyherbert, @jrobeson for contributing to this release.