Restore the document titles dropped when the pages were ported

pom.xml

@@ -5,7 +5,7 @@
   <parent>
     <groupId>org.codehaus.plexus</groupId>
     <artifactId>plexus</artifactId>
-    <version>25</version>
+    <version>26</version>
   </parent>
 
   <artifactId>plexus-io</artifactId>

src/site/markdown/filemappers.md

@@ -1,3 +1,7 @@
+---
+title: File Mappers
+---
+
 # File Mappers
 
 A file mapper is a plexus component, which allows to convert file names. File mappers are used when creating files. For example, the [XML Maven Plugin](https://www.mojohaus.org/xml-maven-plugin) allows to specify a file mapper when creating files by XSLT transformation.

src/site/markdown/fileselectors.md

@@ -1,3 +1,7 @@
+---
+title: File Selectors
+---
+
 # File Selectors
 
 A file selector is a plexus component, which allows to select certain files out of a given set. For example, the [Plexus Archiver](http://plexus.codehaus.org/plexus-archiver) uses file selectors to select the files being archived out of a base directory. Its counterpart, the Plexus Unarchiver allows to restrict the files to unarchive.

src/site/markdown/index.md

@@ -1,3 +1,7 @@
+---
+title: Introduction
+---
+
 # Plexus IO
 
 Plexus IO is a set of plexus components, which are designed for use in I/O operations. These I/O operations are doing nothing spectacular. For example, [Commons IO](http://jakarta.apache.org/commons/io) is a much more powerful library in the same area. However, the implementation as a plexus component allows reuse in Maven.