Update README.md

fixed test

fixed the issue

add main test case

rm example directory

rename example directory to docs

remove uesless example

add convert test case

add scale image example

Add vender

add scale image test cases

add convert package testdata

refactor the convert package

add Example

Remove windows build

Add Converalls Badge

Update travis ci config file to support converalls

Add Cover badge

Test sub packages

Add test case cover