Update some feature examples

(cherry picked from commit 1dca14a)

kotlin-features/concise.md

@@ -9,7 +9,7 @@ data class Customer(val name: String, val email: String, val company: String)
 Or filter a list using a lambda expression:
 
 ``` kotlin
-val positiveNumbers = list.filter {it > 0}
+val positiveNumbers = list.filter { it > 0 }
 ```
 
 Want a singleton? Create an object:

kotlin-features/kotlin-features.yml

@@ -11,7 +11,7 @@
   content_file: versatile.html
 
 - title: Interoperable
-  description: Leverage existing frameworks and libraries of the JVM with 100% Java Interoperability.
+  description: Leverage existing libraries for JVM, Android and the browser with full interoperability.
   content_file: interoperable.md
 
 - title: Tooling

kotlin-features/safe.md

@@ -3,23 +3,22 @@
 Get rid of those pesky NullPointerExceptions, you know, The Billion Dollar Mistake
 
 ``` kotlin
-var output : String
-output = null
+var output: String
+output = null   // Compilation error
 ```
 
-And of course, Kotlin protects you from mistakenly operating on nullable types,
-including those from Java
+Kotlin protects you from mistakenly operating on nullable types
 
 ``` kotlin
-println(output.length())
+val data: String? = null    // Nullable type
+println(data.length())      // Compilation error
 ```
 
 And if you check a type is right, the compiler will auto-cast it for you
 
 ``` kotlin
 fun calculateTotal(obj: Any) {
-    if (obj is Invoice) {
+    if (obj is Invoice)
         obj.calculateTotal()
-    }
 }
 ```