Fix ellipsis encoding in the text layout

[penguinolog]

• Use ... substitution in case of … encoding fails and cache result
• • do not encode multiple times the same value
• • handle unsupported encodings
    Fix: Ellipsis wrap mode is supported only for UTF and limited list of other encodings #496

Checklist

• I've ensured that similar functionality has not already been implemented
• I've ensured that similar functionality has not earlier been proposed and declined
• I've branched off the master or python-dual-support branch
• I've merged fresh upstream into my branch recently
• I've ran tox successfully in local environment
• I've included docstrings and/or documentation and/or examples for my code (if this is a new feature)

[coveralls]

Pull Request Test Coverage Report for Build 7928555744

Details

• 0 of 19 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.1%) to 71.213%

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Totals
Change from base Build 7927756327:	0.1%
Covered Lines:	8925
Relevant Lines:	12631

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💛 - Coveralls

[AnonymouX47]

EDIT: Never mind... Will open a new issue.

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CanvasError is raised when ... (triple period) is used and 1 <= maxcols < 3 e.g

import urwid
urwid.set_encoding("ascii")
text = urwid.Text("Cool", wrap="ellipsis")
text.render((2,))

results in

urwid.canvas.CanvasError: Canvas text is wider than the maxcol specified:
maxcol=2
widths=[3]
text=[b'...']
urwid target encoding=ascii

Might also want to include these edge cases in the tests.

Thanks for your work!