Plan to drop support for Python 2.7

[hugovk]

Python 2.7 (and therefore all Python 2) reaches EOL on January 1st, 2020.

• Update Python 2.7 EOL date python/devguide#344
• https://pythonclock.org
• http://python3statement.org

OSMViz 3.x will drop support for Python 2.7 before that, perhaps this year. There will still be an installable Python 2.7 version on PyPI (OSMViz 2.x), but no further updates will be made for 2.7.

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Here's the pip installs for OSMViz from PyPI for May 2018:

python_version	percent	download_count
2.7	52.27%	46
3.5	18.18%	16
3.4	18.18%	16
3.6	11.36%	10
Total		88

Source: pypinfo --start-date 2018-05-01 --end-date 2018-05-31 --percent --markdown osmviz pyversion

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Pre-drop:

• setuptools >= 24.3
• pip >= 9.0.1
• Update docs and scripts to use pip
• Runtime warning on master, link here
• Pre-drop release

Drop:

• Fail early at import time
• Fail early in setup.py
• Remove Python 2 code
• Update python_requires and Trove classifiers
• Change deprecation warning to error
• Bump major version to 3.0
• Release

[hugovk]

OSMViz 2.1.0 with a deprecation warning for Python 2 is released.

Python 2 support has been removed from master and will be released as OSMViz 3.0.0 at some point.

[hugovk]

OSMViz 3.0.0 released.