Support displaying the dot character in SegmentDisplay.

[mum4k]

Fixes #183

Steps:

• Factor code common to multiple segment display types out of the sixteen package.
• Create a new segment display type that can display a dot and a colon.
• Update SegmentDisplay to use the new display type.

[coveralls]

Pull Request Test Coverage Report for Build 1115

• 211 of 238 (88.66%) changed or added relevant lines in 8 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.1%) to 92.456%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
internal/segdisp/segdisp.go	31	33	93.94%
internal/segdisp/dotseg/dotseg.go	84	90	93.33%
widgets/segmentdisplay/segmentdisplay.go	17	26	65.38%
internal/segdisp/dotseg/attributes.go	46	56	82.14%

Files with Coverage Reduction	New Missed Lines	%
widgets/segmentdisplay/segmentdisplay.go	1	85.71%

Totals
Change from base Build 1107:	-0.1%
Covered Lines:	7280
Relevant Lines:	7874

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💛 - Coveralls