Podspec from current repo

Addresses https://github.com/Tabbedout/SodiumObjc/issues/4
After posting my issue I saw that @iltercengiz has already forked this project [here](https://github.com/iltercengiz/SodiumObjc) and created a podspec for it. He also fixed a resulting compiling problem (that comes from not including files as `"sodium/xyz.h"` but as `<sodium/xyz.h>`). He also made some other changes I did not quite understand and don't think are necessary. 
I took your current repository, added his podspec and include fixes, and then changed his Podspec to point to TabbedOut's original repository and hope that this might be useful for someone. Installing SodiumObjc in my project was just adding 
```
pod "SodiumObjc", :git => https://github.com/r-arias/SodiumObjc.git
```
to the podfile for me and should work using your repository, once you decide to merge this in.
You should check whether the version "1.1" is correct.
Credit for this definitely should go to @iltercengiz.