Ensure HUD overlayWindow is visible above other windows.

Even without creating other windows, in some cases (it depends on how iOS is displaying the windows) the HUD's overlayWindow won't be visible. The display of windows with the same level doesn't appear to be guaranteed, so we should position the HUD at a higher level to guarantee visibility.
Added an implementation of UIAppearance
Remove dealloc completely (singletons don't need one: http://stackoverflow.com/questions/5010701).
Update keyboard view finding code for iOS 6.
added ring progress HUD
Merge pull request #104 from jcoleman/master

Ensure HUD overlayWindow is visible above other windows.
Update key window when dismissing HUD (thanks wvdhaute).
Merge branch 'master' of github.com:samvermette/SVProgressHUD
Merge branch 'master' of https://github.com/lifedim/SVProgressHUD
Remove empty groups from project.
Add progress tracking methods (finally!):

+ (void)showProgress:(CGFloat)progress;
+ (void)showProgress:(CGFloat)progress status:(NSString*)status;
+ (void)showProgress:(CGFloat)progress status:(NSString*)status maskType:(SVProgressHUDMaskType)maskType;
Fix bug with ring showing when calling one of the dismiss methods.
Update Read me.
Use GitHub syntax highlighting.
Switch Read me to Markdown.
Make new progress indicator same size as activity indicator.
Simplify and update Read me with new screenshot.
Restore background ring layer.
Fix compile warning.
Fixed bug with repeated pressing of showWitProgress button