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