add Mini-Circuits AH202-1 & land pattern PL-246

This adds the Mini-Circuits package AH202-1 and a land pattern PL-246 for this package.

The package is a bit of a mess, so here some comments on my thoughts:

• The pads were all created in imperial dimensions as they partially do not exist in metric. The outline (fab layer, silk, etc.) were created using the metric dimensions given in the datasheet.
• I made separate pads for 2 & 3 and 5 & 6 even though they touch. But otherwise there would be gaps in the pin numbering.
• At least according to the package the index is on top of pin 8. I added a similar dot to the silk layer and fab layer. Is this correct/acceptable? I also mad an indication of pin 1 by shortening the silk line there.
• For the land pattern I filled the missing dimensions with those from the land pattern of the package.
• For the land pattern I placed the paste manually on the central cross-like section. The coverage is between 60 and 65%, I tried to stay away from the vias:

Screenshots of the footprints:

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All contributions to the kicad library must follow the KiCad library convention

Thanks for creating a pull request to contribute to the KiCad libraries! To speed up integration of your PR, please check the following items:

• Provide a URL to a datasheet for the footprint(s) you are contributing
• An example screenshot image is very helpful
• If there are matching symbol or 3D model pull requests, provide link(s) as appropriate
• Check the output of the Travis automated check scripts - fix any errors as required
• Give a reason behind any intentional library convention rule violation.