added supporting users http headers for file downloading
any usability changes
validating setting for XCode 5
fixed misspelled property, properties should not be mutable
restored previous setting of Range header. fixed misspelled property name, property dictionary should not be mutable
removed unneeded onceToken
code style
Fixed missing - in travis.yml
Merge branch 'sstepashka-master' of github.com:Cocoanetics/DTDownload into develop

Conflicts:
	DTDownload.xcodeproj/project.pbxproj
Fixed project structure for Demo