Fix some document error.
Fix a mismatch description.
Adjust indenting.
Format code in document.
Merge pull request #400 from BB9z/fix/document-parameter

Some document improves.
Update SDWebImageCompat.h

Undefine macros before define to prevent warning on iOS
Merge pull request #401 from docallag/master

Prevent warnings on iOS
Fix typo in download page URL
#406 - Fixed a problem where hitting a failed URL more than once wouldn't call the completion block
Merge pull request #408 from dlbuckley/issue-406-Failed-URL-Problem

#406 - Fixed failed URL problem
Merge pull request #1 from rs/master

merge author update