pkg -- handle mydumper data source (pingcap#3)

* pakage for handle mydumper data source

* modify mydump reader implementation of reading block content

* 1. error check
2. fix problem of block reading
3. modify test cases

* return error on failed creating loader

* mydumper reader's method *Read* accepts 'minBlockSize' rather than 'maxBlockSize' as batch size limitation.

* regulate spelling mistake

* regulate spelling mistake

* update expression of judging valid myduper table file by checking file-name

ingest/mydump/const.go

@@ -0,0 +1,5 @@
+package mydump
+
+const (
+	defReadBlockSize int64 = 1024 * 8
+)

ingest/mydump/examples/metadata

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+Started dump at: 2017-11-30 20:16:38
+Finished dump at: 2017-11-30 20:16:38

ingest/mydump/examples/mocker_test-schema-create.sql

@@ -0,0 +1 @@
+CREATE DATABASE `mocker_test` /* !40100 DEFAULT CHARACTER SET utf8 */;

ingest/mydump/examples/mocker_test.tbl_autoid-schema.sql

@@ -0,0 +1,8 @@
+/*!40101 SET NAMES binary*/;
+/*!40014 SET FOREIGN_KEY_CHECKS=0*/;
+
+CREATE TABLE `tbl_autoid` (
+  `ID` int(10) UNSIGNED NOT NULL AUTO_INCREMENT,
+  `Name` varchar(64) DEFAULT NULL,
+  PRIMARY KEY (`ID`)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin;