Merge pull request #50 from p0deje/master

Release v1.4
added User#embed_key!, User#providers!, User#roles!
Fix code comments, fix user_spec, add GroupDocs::Storage::Provider and spec for it, make User#providers! as class method
fix code style, fix example for embed_key! method
replace tabs with spaces
Merge pull request #51 from averjr/master

Add few User methods
Update 18th sample with callback, add htm samples for 18th sample, update css, add images for css.
Merge branch 'master' of github.com:groupdocs/groupdocs-ruby