Add 3.81mm tht diode footprints

[evanshultz]

2.54mm is too small to run a trace between the pads, and 5.08 is excessively wide if only a thin trace (0.25mm, 0.5mm, etc.) is desirable to run between the pads.

Images:

Script update at pointhi/kicad-footprint-generator#153.

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• Provide a URL to a datasheet for the footprint(s) you are contributing
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• If there are matching symbol or 3D model pull requests, provide link(s) as appropriate
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[poeschlr]

I looked at the changes of the script. Looks good to me.

You also changed a datasheet link. This change however is not included here. Could you add a separate PR that updates this in the affected footprints?