Drop support for legacy Python 2.7

[hugovk]

Fixes #650.

Adds python_requires to help pip.

Also upgrade syntax with https://github.com/asottile/pyupgrade and unit tests to use more useful asserts.

[codecov-io]

Codecov Report

Merging #654 into master will decrease coverage by 0.06%.
The diff coverage is 73.47%.

@@            Coverage Diff             @@
##           master     #654      +/-   ##
==========================================
- Coverage   71.84%   71.77%   -0.07%     
==========================================
  Files          49       49              
  Lines       15814    15804      -10     
==========================================
- Hits        11361    11343      -18     
- Misses       4453     4461       +8

Impacted Files	Coverage Δ
androguard/decompiler/dad/util.py	64.36% <0%> (ø)	⬆️
androguard/decompiler/dad/dataflow.py	98.7% <100%> (ø)	⬆️
androguard/decompiler/dad/graph.py	91.11% <100%> (ø)	⬆️
tests/dataflow_test.py	93.93% <100%> (ø)	⬆️
tests/rpo_test.py	97.8% <100%> (ø)	⬆️
tests/test_arsc.py	98.85% <100%> (ø)	⬆️
androguard/decompiler/decompiler.py	27.25% <100%> (ø)	⬆️
tests/test_analysis.py	98.79% <100%> (ø)	⬆️
androguard/decompiler/dad/dast.py	13.69% <100%> (ø)	⬆️
androguard/decompiler/dad/opcode_ins.py	87.34% <100%> (ø)	⬆️
... and 20 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 07428e3...85cc1b9. Read the comment docs.

[reox]

Do you know if there are narrow 3.x builds? otherwise we can remove this too...

[hugovk]

I don't know.

[reox]

Wow, this looks very nice!
To summarize what you did:

• replace all super(Classname, self.)... with super()
• remove all (object) from class definitions
• replace C string fmt with propper .format
• add regex type string if not present
• remove all unicode string definitions
• change set() to {}

There are also import from future and builtins which could be removed now, as they were primary for the py2/3 compatability.
Also the one comment: This was a fix for narrow 2.x builds, but I think there are no narrow py3 builds? At least according to SO (https://stackoverflow.com/questions/14790708/do-unicode-strings-in-python-3-still-depend-on-narrow-wide-builds) this only affects up to 3.2. But as our minimal version is 3.4 (due to other issues) we should be fine.

This PR sounds like, that the next version will be 4.0.0 ;)

[reox]

@androguard/external-contributors please have a look!

[eighthave]

Most of the changes look simple and good. Changing the formats could cause breakage, so I hope those cases are covered by tests.

[reox]

so I hope those cases are covered by tests.

so far, the tests work for mutf8 parsing - which was one of the most annoying things to have both working for py2 and py3.