Adding Podspec for Swift 4 support (Krisiacik#158)

* Bumping podspec

This is to incorporate the Swift 4 support that was merged into master.

* Updating podspec to 5.0.0

Since the Swift 4 upgrade was a breaking change, we're bumping this to 5.0.0 instead of 4.2.0.

* Updating README to reflect Swift 4/ImageViewer 5

Merge pull request Krisiacik#60 from JoeFerrucci/version-fix

Correct version

Added a nature based video.

Merge pull request Krisiacik#44 from zfoltin/gallery-see-all

Gallery - See All - thumbnails FTW!

Fixed a crash caused by KVO observer handling.

Merge pull request Krisiacik#29 from MailOnline/ka/ProgramaticClose

Ka/Programatic close support

Merge pull request Krisiacik#28 from MailOnline/ka/FooterViewLayoutFix

ka/LayoutFix

Fixes github issue Krisiacik#26 with swipe to dismiss to bottom not f…

…inishing.