Xcode 8 warnings fixed.

1.0.7

- fixed Xcode 8 warnings.

fixed the cancel download bug

fixed the cancel download bug

Added documentation for all header files.

1.0.5

changed to version 1.0.5

added notifications for start and stop image download

1.0.4

- fixed notification bug where addObserver's object property was self…

changed urlString to be nullable

urlString was changed to __nullable so it doesn't required nil check with Swift every time a urlString is set.

Added __nullable and __nonnull type annotations for the headers.

1.0.2

- added __nullable and __nonnull type annotations for the headers.

1.0.0

- added LICENSE.md file