Drop Python 2 and 3.4: Update Metadata, ChangeLog

This starts a series of commits to drop support for Python 2 and 3.4 as
discussed in [pydot#171][171] and [pydot#229][229].

| Python version | Python EOL | PyPI 2020-05-02 | PyPI 2021-06-21 |
|----------------|------------|-----------------|-----------------|
| Python 2.7     | 2020-01-01 |             26% |             12% |
| Python 3.4     | 2019-03-18 |              0% |              0% |
| Python 3.5     | 2020-09-30 |             27% |              3% |
| Python 3.6     | 2021-12    |             21% |             14% |
| Python 3.7     | 2023-06    |             23% |             51% |
| Python 3.8     | 2024-10    |              3% |             13% |
| Python 3.9     | 2025-10    |              0% |              6% |
| Python 3.10    | 2026-10    |               - |              0% |

EOL : End of life, from End of security support on [Wikipedia][1].
PyPI: Python Package Index statistics for pydot from [PyPIstats.org][2].

Without support for Python 2, wheel distributions of pydot can [no
longer be marked as "universal"][3], so removing that from `setup.cfg`.

**USER FEEDBACK REQUESTED**
We are considering if pydot 2.0 should drop support for Python 3.5
and 3.6 as well. If this would affect you, please leave a comment in
[pydot#268][268].

[1]: https://en.wikipedia.org/w/index.php?title=History_of_Python&oldid=1022680403#Table_of_versions
[2]: https://pypistats.org/packages/pydot
[3]: https://github.com/pypa/packaging.python.org/blob/44313e5db4d729eede0bcb91c08d6ec93e89c5c8/source/guides/dropping-older-python-versions.rst#dealing-with-the-universal-wheels
[171]: pydot#171 (comment)
[229]: pydot#229
[268]: pydot#268

ChangeLog

@@ -7,7 +7,12 @@ Pydot versions since 1.4.2 adhere to [PEP 440-style semantic versioning]
 2.0.0 (unreleased)
 ------------------
 
-- Nothing changed yet.
+Removed:
+- Drop support for Python 2 and Python 3.4.
+  **USER FEEDBACK REQUESTED**
+  We are considering if pydot 2.0 should drop support for Python 3.5
+  and 3.6 as well. If this would affect you, please leave a comment in
+  https://github.com/pydot/pydot/issues/268.
 
 
 1.4.2 (2021-02-15)

setup.cfg

@@ -1,6 +1,3 @@
-[bdist_wheel]
-universal=1
-
 [zest.releaser]
 python-file-with-version = pydot.py
 release=no

setup.py

@@ -45,18 +45,15 @@ def get_version():
     license="MIT",
     keywords="graphviz dot graphs visualization",
     platforms=["any"],
-    python_requires=">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*",
+    python_requires=">=3.5",
     classifiers=[
         "Development Status :: 5 - Production/Stable",
         "Intended Audience :: Developers",
         "Intended Audience :: Science/Research",
         "License :: OSI Approved :: MIT License",
         "Natural Language :: English",
         "Operating System :: OS Independent",
-        "Programming Language :: Python :: 2",
-        "Programming Language :: Python :: 2.7",
         "Programming Language :: Python :: 3",
-        "Programming Language :: Python :: 3.4",
         "Programming Language :: Python :: 3.5",
         "Programming Language :: Python :: 3.6",
         "Programming Language :: Python :: 3.7",