Enhance format documentation

- Stub section for "arrayjson" (#96)
- Add references to wikipedia articles for most formats
- Document "shapefile" format
- Add note about numerical rounding in JSON format (#113)

Author: Sandro Santilli

doc/API.md

@@ -12,7 +12,7 @@ Supported query string parameters:
 
   'format':   Specifies which format to use for the response.
               Supported formats: JSON (the default), GeoJSON,
-              TopoJSON, CSV, SVG, SHP
+              TopoJSON, CSV, SVG, SHP, arraybuffer
 
   'filename': Sets the filename to use for the query result 
               file attachment
@@ -37,6 +37,9 @@ Supported query string parameters:
 Response formats
 ----------------
 
+
+### JSON
+
 The standard response from the CartoDB SQL API is JSON. If you are
 building a web-application, the lightweight JSON format allows you to
 quickly integrate data from the SQL API.
@@ -69,6 +72,12 @@ The JSON response is as follows:
     }
 ```
 
+Note that values of numerical fields will be rounded to at most 16 significant
+digits due to a limit in the JSON format itself. If more precision is needed
+the caller can cast those fields to text using SQL constructs.
+
+### GeoJSON
+
 Alternatively, you can use the GeoJSON specification for returning data
 from the API. To do so, simply supply the format parameter as GeoJSON.
 
@@ -99,7 +108,37 @@ The GeoJSON response is follows:
     }
 ```
 
-TODO: csv, kml, svg, topojson responses
+### CSV
+
+CSV export format has field names in first line (header),
+uses CR/NL line endings and EWKT format for geometri fields.
+
+See https://github.com/postgis/postgis/blob/svn-trunk/doc/ZMSgeoms.txt#L173
+
+### KML
+
+See http://en.wikipedia.org/wiki/KML
+
+### SVG
+
+See http://en.wikipedia.org/wiki/SVG
+
+### TopoJSON
+
+See http://en.wikipedia.org/wiki/Topojson
+
+### SHP
+
+Shapefile output composed by .shp, .shx, .dbf and .prj files
+compressed in a .zip.
+
+See http://en.wikipedia.org/wiki/Shapefile
+
+### Arraybuffer
+
+An octet stream binary-encoding each field as a typed array of value.
+TODO: write more about this format
+See http://github.com/CartoDB/CartoDB-SQL-API/issues/96
 
 Response errors
 ---------------