Create a "Spatial Objects" reference page

[rmloveland]

Richard Loveland (rmloveland) commented:

We will need to provide a list of the spatial object types we support. The list is:

• POINT
• MULTIPOINT
• LINESTRING
• MULTILINESTRING
• POLYGON
• MULTIPOLYGON
• GEOMETRYCOLLECTION

For each object type, we will need to say something about:

• What functions operate on it / take it as input/output etc
• How they are defined
• Which to use when (?)
• Probably other things

Jira Issue: DOC-622