Svg.path

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- Two new test files were omitted from the distributions.

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- Drop Python 2 support, also 3.4 to 3.6. New minimum Python version is 3.7.

- New parser that solves the issue with Arc flags and whitespace.
See Issues 53 and 69.

- Fixed 60: Handle paths that are length 0 [Thanks to martinleopold and tatarize]

- New method on path objects: `.tangent(point)`, which returns a vector that is the
derivatative / tangent of the curve at that point. [vidstige]

- New graphical test. That test requires Pillow, so I stopped testing on PyPy, it
got too complicated to support. But it still works on PyPy.

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- Use collections.abc for ABC import to add Python 3.9 compatibility.

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- A solution for the setup.cfg [Alex Grönholm]

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else:
raise

- The pure setup.cfg config didn't work. All the tests pass fine,
but when installing the package somewhere else, nothing gets installed.
So I'm reverting that change for now.

----------------

- Moved all the information from setup.py into setup.cfg.

- Added a Close() command which is different from a Line() command in
no way at all, to simplify the handling of closepath commands and subpaths.

- Path()'s no longer have a `closed` attribute.

- Now fully supports the SVG 1.1 "F.6.2 Out-of-range parameters" list.

- Uses circular maths to calculate the length of circular arcs,
more accurate and much faster.