Enhanced heading styles for ISO

Also corrected an XML typo

Author: Hanno Klein

v1-0-STANDARD/doc/01Introduction.md

@@ -76,7 +76,7 @@ and data examples.
 This is a sample encoding specification
 
 ```xml
-<type name="short" primitiveType="int16" semanticType="int" />
+<type name="short" primitiveType="int16" semanticType="int"/>
 ```    
 
 This is sample data as it would be transmitted on the wire

v1-0-STANDARD/doc/03MessageStructure.md

@@ -29,7 +29,7 @@ be encoded in big-endian byte order, also known as network byte order.
 Simple Open Framing Header as an SBE composite encoding (big-endian)
 
 ```xml
-<composite name="framingHeader"/>
+<composite name="framingHeader">
     <type name="messageLength" primitiveType="uint32" />
     <type name="encodingType" primitiveType="uint16" />
 </composite>