Add Softball Field preset

[quincylvania]

A softball field has different dimensions than a baseball field, and often has a dirt infield. Softball fields are common in the U.S., especially around schools and universities.

Note: there is currently a page for a baseball=softball tag. This proposal does not appear to be widely accepted and has fewer uses than sport=softball, so I'm ignoring it for now.

• Path: leisure/pitch/softball
• Name: Softball Field
• Geometry: point, area
• Fields: name, lit, possibly others
• Tags: "leisure"="pitch", "sport"="softball"
• Reference: "key": "sport", "value": "softball"
• Terms: softball diamond
• Icon: maki-baseball

[s-Hale]

Added :)