Added methods to implement sql related interfaces.

Version.Scan -> database/sql.Scanner
Version.Value -> database/sql/driver.Valuer

Closes #4
Closes #5

sql.go

@@ -0,0 +1,31 @@
+package semver
+
+import (
+	"database/sql/driver"
+	"fmt"
+)
+
+// Scan implements the database/sql.Scanner interface.
+func (v *Version) Scan(src interface{}) (err error) {
+	var strVal string
+	switch src.(type) {
+	case string:
+		strVal = src.(string)
+	case []byte:
+		strVal = string(src.([]byte))
+	default:
+		return fmt.Errorf("Version.Scan: cannot convert %T to string.", src)
+	}
+
+	tmpv, err := Parse(strVal)
+	if err != nil {
+		return
+	}
+	*v = *tmpv
+	return
+}
+
+// Value implements the database/sql/driver.Valuer interface.
+func (s Version) Value() (driver.Value, error) {
+	return s.String(), nil
+}

sql_test.go

@@ -0,0 +1,38 @@
+package semver
+
+import (
+	"testing"
+)
+
+type scanTest struct {
+	val         interface{}
+	shouldError bool
+	expected    string
+}
+
+var scanTests = []scanTest{
+	scanTest{"1.2.3", false, "1.2.3"},
+	scanTest{[]byte("1.2.3"), false, "1.2.3"},
+	scanTest{7, true, ""},
+	scanTest{7e4, true, ""},
+	scanTest{true, true, ""},
+}
+
+func TestScanString(t *testing.T) {
+	for _, tc := range scanTests {
+		s := &Version{}
+		err := s.Scan(tc.val)
+		if tc.shouldError {
+			if err == nil {
+				t.Fatalf("Scan did not return an error on %v (%T)", tc.val, tc.val)
+			}
+		} else {
+			if err != nil {
+				t.Fatalf("Scan returned an unexpected error: %s (%T) on %v (%T)", tc.val, tc.val, tc.val, tc.val)
+			}
+			if val, _ := s.Value(); val != tc.expected {
+				t.Errorf("Wrong Value returned, expected %q, got %q", tc.expected, val)
+			}
+		}
+	}
+}