#6 Adds support for US and SI units

[Rick]

Add support for US and SI units by enhancing the Units
page of the Preferences dialog and a FormatDistance
function that takes a distance in miles and returns a
string with the distance converted to miles, feet,
kilometers, or meters, as appropreate, along with a
unit tag.

[Rick]

Units Patch File

[Richard Lynch]

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Thank you.

Applied to CVS.