Drop unsupported Python 3.3

[hugovk]

EOL since 2017-09-29:
https://en.wikipedia.org/wiki/CPython#Version_history

See also #44 which fixes the flake8 error for Python 3.5 on the CI.

[hugovk]

pip install from PyPI for the last month:

$ pypinfo --pip --percent inflect pyversion
python_version percent download_count
-------------- ------- --------------
2.7              76.9%         49,561
3.5               9.9%          6,413
3.6               9.0%          5,788
3.4               3.7%          2,414
3.3               0.3%            188
2.6               0.1%             61
3.7               0.0%             29
3.2               0.0%             12

[jaraco]

Sounds reasonable. Let's do this in a backward-incompatible release after the 0.3 release.

[coveralls]

Pull Request Test Coverage Report for Build 21

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 99.067%

---

Totals
Change from base Build 19:	0.0%
Covered Lines:	1168
Relevant Lines:	1179

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 21

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 99.067%

---

Totals
Change from base Build 19:	0.0%
Covered Lines:	1168
Relevant Lines:	1179

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 25

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 99.067%

---

Totals
Change from base Build 19:	0.0%
Covered Lines:	1168
Relevant Lines:	1179

---

💛 - Coveralls

[hugovk]

Resolved merge conflict, and upgraded Python syntax using https://github.com/asottile/pyupgrade.

[hugovk]

Sounds reasonable. Let's do this in a backward-incompatible release after the 0.3 release.

@jaraco 0.3 has been released. Can this be merged? Thanks!