issue0003: md5 & file size verfiy

1.verify file md5 when download end, if md5 is mismatch, task will be cancel
2.check the fileSize of input, if the fileSize is set, the download service will not query remote file size before download
3.fixbug: delete the work queue instead wait queue when download finish

Change-Id: I34101b452fd813626f21662630bb1887c687eee6
issue0004: compelete Pause && Resume

1. Compelete Pause and Resume Task Function
2. Remove blank of README.MD and Fix the speed unit as Bit/s

Change-Id: I0cda6c1590e088514bde22daf89deaf467935e7d
Merge branch 'master' into develop

Conflicts:
	test/service_test.go

Change-Id: I426140d79fece3da7631fa585c1f6d39a42ff9fc