test/data/geohash.ics: Pull out geohashing example from Feed doctest

test/data/geohash.ics: Pull out geohashing example from Feed doctest

This makes it easier to reuse the test data in other locations.

Also escape commas in the data.  From RFC 5545, section 3.3.11. Text:

  The "TEXT" property values may also contain special characters that
  are used to signify delimiters, such as a COMMA character for lists
  of values or a SEMICOLON character for structured values.  In order
  to support the inclusion of these special characters in "TEXT"
  property values, they MUST be escaped with a BACKSLASH character.