concurrency support, closes #20 and closes #9 and closes #15

* c600769 do not require a connection name, unique dsn is generated
* 1b20b9c update travis
* 1097b6a add comments for godoc documentation
* c142a95 fix golint reported issues

statement.go

@@ -5,12 +5,13 @@ import (
 )
 
 type statement struct {
-	conn  *conn
+	conn  *Sqlmock
 	query string
+	err   error
 }
 
 func (stmt *statement) Close() error {
-	return nil
+	return stmt.err
 }
 
 func (stmt *statement) NumInput() int {