Added capability to use lib as a static framework (#60)

Co-authored-by: Gleb Volchetskiy <g.volchetskiy@wowmaking.net>

Author: qvick1pro

README.md

@@ -63,6 +63,10 @@ You can find available versions [here](https://github.com/wowmaking/react-native
   1. Add `pod 'RNIronSource', :path => '../node_modules/@wowmaking/react-native-iron-source'` to your `ios/Podfile`
   2. Run `pod install` while in `ios` directory
 
+  #### Allow iOS Static Frameworks
+  If you are using Static Frameworks on iOS, you need to manually enable this for the project. To enable Static Framework support, add the following global to the top of your /ios/Podfile file:
+  `$RNIronSourceAsStaticFramework = true`
+
   ##### Android
 
   1. Open up `android/app/src/main/java/[...]/MainApplication.java`

RNIronSource.podspec

@@ -68,4 +68,11 @@ Pod::Spec.new do |s|
     ss.dependency         "IronSourceVungleAdapter", "> 1"
   end
 
+  if defined?($RNIronSourceAsStaticFramework)
+    Pod::UI.puts "#{s.name}: Using overridden static_framework value of '#{$RNIronSourceAsStaticFramework}'"
+    s.static_framework = $RNIronSourceAsStaticFramework
+  else
+    s.static_framework = false
+  end
+
 end