Update example podfiles to current format. Maybe it’s better to have a separate…

Update example podfiles to current format. Maybe it’s better to have a separate API/DSL for a podfile after all, so that this isn't necessary.

examples/AFNetworking Example/Podfile

-dependency 'AFNetworking'
-dependency 'FormatterKit'
+Pod::File.new do |f|
+  f.platform = :ios
+  f.dependency 'AFNetworking'
+  f.dependency 'FormatterKit'
+end

examples/MGSplitViewController/Podfile

-dependency 'MGSplitViewController', '1.0.0'
+Pod::File.new do |f|
+  f.platform = :ios
+  f.dependency 'MGSplitViewController', '1.0.0'
+end

examples/RKTwitter/Podfile

-dependency 'RestKit-ObjectMapping'
-dependency 'RestKit-JSON-JSONKit'
+Pod::File.new do |f|
+  f.platform = :ios
+  f.dependency 'RestKit-ObjectMapping'
+  f.dependency 'RestKit-JSON-JSONKit'
+end