Python-petpptx

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- Fix module 'collections' has no attribute 'Container' for latest python 3.10

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- Release of a new version of the project
- Add setter for font in Run

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- Fix 741 _DirPkgReader must implement .__contains__()

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- Fix 206 accommodate NULL target-references in relationships.
- Fix 223 escape image filename that appears as literal in XML.
- Fix 517 option to display chart categories/values in reverse order.
- Major refactoring of ancient package loading code.

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- Add shapes.add_ole_object(), allowing arbitrary Excel or other binary file to be
embedded as a shape on a slide. The OLE object is represented as an icon.

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- .text property getters encode line-break as a vertical-tab (VT, '\v', ASCII 11/x0B).
This is consistent with PowerPoint's copy/paste behavior and allows like-breaks (soft
carriage-return) to be distinguished from paragraph boundary. Previously, a line-break
was encoded as a newline ('\n') and was not distinguishable from a paragraph boundary.

.text properties include Shape.text, _Cell.text, TextFrame.text, _Paragraph.text and
_Run.text.

- .text property setters accept vertical-tab character and place a line-break element in
that location. All other control characters other than horizontal-tab ('\t') and
newline ('\n') in range \x00-\x1F are accepted and escaped with plain-text like
"_x001B" for ESC (ASCII 27).

Previously a control character other than tab or newline in an assigned string would
trigger an exception related to invalid XML character.