Added .podspec and implemented initWithView

Hi there and thanks for your work!

I'd like to suggest the following changes which are self-explanatory by commit messages.

I used them to initiate your brilliant SuProgressBar in my view, not navigation bar.

Also the podspec is added in order to point my other project Podfile to my fork by using the following string:
```
pod 'SuProgress', :git => 'https://github.com/DZamataev/SuProgress.git', :branch => 'master'
```