Extract complex expression to help JDK 8 make sense of the Java types

Full explanation:
JDK 8 doesn't realize we want to handle a stream of `JApiCompatibility`
elements. Instead, the compiler thinks we want to create a stream of
`JApiHasChangeStatus` elements. So I just extracted the complex
expression to a constant with the appropriate type and it works fine.

Other JDK versions get it right without the type hint. ¯\_(ツ)_/¯

Root cause of the problem:

```
Caused by: java.lang.invoke.LambdaConversionException: Invalid receiver type interface japicmp.model.JApiHasChangeStatus; not a subtype of implementation type interface japicmp.model.JApiCompatibility
	at java.lang.invoke.AbstractValidatingLambdaMetafactory.validateMetafactoryArgs(AbstractValidatingLambdaMetafactory.java:233)
	at java.lang.invoke.LambdaMetafactory.metafactory(LambdaMetafactory.java:303)
	at java.lang.invoke.CallSite.makeSite(CallSite.java:302)
	... 54 more
```

japicmp/src/main/java/japicmp/output/markdown/MarkdownOutputGenerator.java

@@ -384,7 +384,7 @@ private final String renderCompatibilityChanges(List<? extends JApiCompatibility
 	}
 
 	private String renderAllCompatibilityChanges(JApiClass clazz) {
-		return renderCompatibilityChanges(Stream.of(
+		final Stream<List<? extends JApiCompatibility>> allCompatibilityChanges = Stream.of(
 				singletonList(clazz),
 				singletonList(clazz.getClassFileFormatVersion()),
 				singletonList(clazz.getSuperclass()),
@@ -397,7 +397,8 @@ private String renderAllCompatibilityChanges(JApiClass clazz) {
 				clazz.getMethods(),
 				clazz.getMethods().stream().map(JApiMethod::getReturnType).collect(toList()),
 				clazz.getMethods().stream().map(JApiMethod::getParameters).flatMap(List::stream).collect(toList()),
-				clazz.getFields())
+				clazz.getFields());
+		return renderCompatibilityChanges(allCompatibilityChanges
 			.flatMap(List::stream)
 			.map(JApiCompatibility::getCompatibilityChanges)
 			.flatMap(List::stream)