add methods for replace from other modules
update README.md
delete unused swizzling code
add properry `keepRequest`

- If you dont kill a reqest, cache image with it.
consider this thread is main thread in block
revert property, `completionHash` to `imageLoaderCompletionKey`
fix warning
Merge branch 'master' into 0.1.1
Merge pull request #1 from hirohisa/0.1.1

0.1.1