This PR migrates a couple of functions to the new documentation layout.

Few questions for discussion:

• Should we make each page expansive with a good conceptual overview of the function and many examples? I feel like it would be great to have a page that explains functions like ST_Area in detail and provides many examples. Here's the PostGIS ST_Area page that is fairly detailed.
• Should we take it to the next level and help newer users understand the related functions? We could explain ST_AreaSpheroid and
• Should we add a since flag in the frontmatter?
• Can we add some frontmatter with updates? e.g. some way to denote what version the use_spheroid arg is added to ST_Area.

The new SQL doc framework is awesome!!