Upgrade pdfminer.six from 20200517 to 20211012

[jsvine]

See pdfminer.six's changelog for details: https://github.com/pdfminer/pdfminer.six/blob/develop/CHANGELOG.md

... but a key difference is an improvement in how it assigns line, rect, and curve objects. (Diagonal two-point lines, for instance, are now line objects instead of curve objects.)

As a result, this commit also adjusts some of the tests, where the pre-20211012 versions had been incorrectly assigning lines as LTCurve objects.

Note: This commit also tweaks CHANGELOG.md to call the next release 0.6.0, since this will be a breaking change for some use-cases — though an improvement, and necessary if we don't want pdfplumber to fall far out of sync with pdfminer.six.

[codecov]

Codecov Report

Merging #515 (5794aaa) into develop (7a65785) will not change coverage.
The diff coverage is n/a.

❗ Current head 5794aaa differs from pull request most recent head 4b61c38. Consider uploading reports for the commit 4b61c38 to get more accurate results

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[samkit-jain]

Long-awaited upgrade. @jsvine Should all the references to the curves property be removed as well if with this uprade, all curves would be lines? For example,

pdfplumber/pdfplumber/container.py

Line 39 in 1328a00

def curves(self):

[jsvine]

Good question, and I can see how that'd be confusing. Curve objects do still exist — they're paths with more than 2 points and which do not constitute a rectangle (or multiple consecutive rectangles). The fixes in the new version of pdfminer.six simply assign "LTLine" correctly in instances where it had previously been assigning "LTCurve," for instance diagonal lines. For an example of some paths that are still correctly curve objects, see the shapes on the final page of this PDF: http://www.pdfill.com/example/pdf_drawing_new.pdf