encoding/wkb: update readme for new mysql functionality

Author: paulmach

encoding/wkb/README.md

@@ -1,45 +1,59 @@
-encoding/wkb [![Godoc Reference](https://godoc.org/github.com/paulmach/orb?status.svg)](https://godoc.org/github.com/paulmach/orb/encoding/wkb)
-============
+# encoding/wkb [![Godoc Reference](https://godoc.org/github.com/paulmach/orb?status.svg)](https://godoc.org/github.com/paulmach/orb/encoding/wkb)
 
 This package provides encoding and decoding of [WKB](https://en.wikipedia.org/wiki/Well-known_text_representation_of_geometry#Well-known_binary)
 data. The interface is defined as:
 
-	func Marshal(geom orb.Geometry, byteOrder ...binary.ByteOrder) ([]byte, error)
-	func MustMarshal(geom orb.Geometry, byteOrder ...binary.ByteOrder) []byte
+    func Marshal(geom orb.Geometry, byteOrder ...binary.ByteOrder) ([]byte, error)
+    func MustMarshal(geom orb.Geometry, byteOrder ...binary.ByteOrder) []byte
 
-	func NewEncoder(w io.Writer) *Encoder
-	func (e *Encoder) SetByteOrder(bo binary.ByteOrder)
-	func (e *Encoder) Encode(geom orb.Geometry) error
+    func NewEncoder(w io.Writer) *Encoder
+    func (e *Encoder) SetByteOrder(bo binary.ByteOrder)
+    func (e *Encoder) Encode(geom orb.Geometry) error
 
-	func Unmarshal(b []byte) (orb.Geometry, error)
+    func Unmarshal(b []byte) (orb.Geometry, error)
 
-	func NewDecoder(r io.Reader) *Decoder
-	func (d *Decoder) Decode() (orb.Geometry, error)
+    func NewDecoder(r io.Reader) *Decoder
+    func (d *Decoder) Decode() (orb.Geometry, error)
 
-### Reading and Writing to a SQL database
+## Reading and Writing to a SQL database
 
 This package provides wrappers for `orb.Geometry` types that implement
 `sql.Scanner` and `driver.Value`. For example:
 
-	row := db.QueryRow("SELECT ST_AsBinary(point_column) FROM postgis_table")
+```go
+row := db.QueryRow("SELECT ST_AsBinary(point_column) FROM postgis_table")
 
-	var p orb.Point
-	err := row.Scan(wkb.Scanner(&p))
+var p orb.Point
+err := row.Scan(wkb.Scanner(&p))
 
-	db.Exec("INSERT INTO table (point_column) VALUES (?)",
-		wkb.Value(p))
+db.Exec("INSERT INTO table (point_column) VALUES (?)", wkb.Value(p))
+```
 
 If you don't know the type of the geometry try something like
 
-	s := wkb.Scanner(nil)
-	err := row.Scan(&s)
+```go
+s := wkb.Scanner(nil)
+err := row.Scan(&s)
 
-	switch g := s.Geometry.(type) {
-	case orb.Point:
-	case orb.LineString:
-	}
+switch g := s.Geometry.(type) {
+case orb.Point:
+case orb.LineString:
+}
+```
 
-Scanning directly from MySQL columns is supported. By default MySQL returns geometry
-data as WKB but prefixed with a 4 byte SRID. To support this, if the data is not
-valid WKB, the code will strip the first 4 bytes, the SRID, and try again.
-This works for most use cases.
+## MySQL or MariaDB
+
+By default MySQL returns geometry data as WKB but prefixed with a 4 byte SRID.
+This is supported using the `MySQLScanner` and `MySQLValue`. For example:
+
+```go
+db.Exec("INSERT INTO geotest(id, geom) VALUES (?, ?)", 1, wkb.MySQLValue(orb.Point{1, 1}))
+```
+
+Reading of MySQL point data is supported using the regular scanner but other types may have issues.
+For best results use `MySQLScanner` to handle the 4 byte SRID prefix.
+
+```go
+var p orb.Point
+rows, err := db.QueryRow("SELECT geom FROM geotest").Scan(wkb.MySQLScanner(p))
+```