Added CK KMR2 series tactile buttons

Hello,

I would like to add the footprint for C&K Components KM2 series Microminiature SMT Top Actuated tactile switches to the 'Button_Switch_SMD' library. I have used other C&K branded buttons in the same library as a guideline for the design of these footprints. There are two footprints, one for the switch with grounding pin, and one without. As there is no symbol in the library for a grounded tactile switch so far (correct me if I'm wrong), I've used the next number (3) for the grounding pin, as this seems to be the convention in other symbol libraries (such as for connectors).

The distance from the pads or F.fab to the F.Courtyard is 0.25mm instead of 0.5mm. This seems to be the default for SMD buttons of this size, based on what I've seen being used with other similar footprints in the same library.

The distance from the pads to F.Silkscreen is 0.12mm for the same reason stated above. Similar footprints seem to use this spacing.

Datasheet: https://www.ckswitches.com/media/1479/kmr2.pdf

The pad sizes are X0.9 x Y1.0mm, as can be deduced from the measurements in the datasheet. 25% rounded edges are used.

The dimensioned footprint:

Checked with the 3D model downloaded from https://www.ckswitches.com/products/switches/product-details/Tactile/KMR2/KMR231GLFS/

Result:

Thanks for reviewing my contribution!