vty: Add xsd and a command that can generate the documentation.

When building the doxygen documentation do not remove the other
VTY documentation files in the doc/vty folder. Create a command
that can be installed to dump all nodes and commands as XML on
the given VTY. Create a schema for the XML file and a XSL-T script
that can merge the generated file with additional information.
diff --git a/doc/vty/example.xml b/doc/vty/example.xml
new file mode 100644
index 0000000..400c634
--- /dev/null
+++ b/doc/vty/example.xml
@@ -0,0 +1,22 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<vtydoc xmlns="urn:osmocom:xml:libosmocore:vty:doc:1.0">
+    <!-- test a nested hierachy -->
+    <node id="mgcp" name="MGCP Node">
+	<!-- define a command -->
+	<command id="foo_cmd">
+		<doc>General docs</doc>
+		<params>
+			<param name="do" doc="Explain do" />
+			<param name="fo" doc="Explain foo" />
+		</params>
+	</command>
+	<command id="foo_cmd">
+		<doc>General docs</doc>
+		<params>
+			<param name="do" doc="Explain do" />
+			<param name="fo" doc="Explain foo" />
+		</params>
+	</command>
+
+    </node>
+</vtydoc>
diff --git a/doc/vty/merge_doc.xsl b/doc/vty/merge_doc.xsl
new file mode 100644
index 0000000..6e1bab1
--- /dev/null
+++ b/doc/vty/merge_doc.xsl
@@ -0,0 +1,37 @@
+<?xml version="1.0" encoding="ISO-8859-1"?>
+<xsl:transform version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
+                             xmlns:vty="urn:osmocom:xml:libosmocore:vty:doc:1.0">
+  <xsl:output method="xml" version="1.0" encoding="ISO-8859-1" indent="yes" />
+  <xsl:variable name="with" select="'additions.xml'" />
+
+  <xsl:template match="@*|node()">
+    <xsl:copy>
+      <xsl:apply-templates select="@*|node()" />
+    </xsl:copy>
+  </xsl:template>
+
+
+  <!-- Copy the name of the node -->
+  <xsl:template match="vty:node">
+    <xsl:copy>
+      <xsl:apply-templates select="@*|node()" />
+      <xsl:variable name="info" select="document($with)/vty:vtydoc/vty:node[@id=current()/@id]/." />
+      <xsl:for-each select="$info/vty:name">
+          <xsl:copy-of select="." />
+      </xsl:for-each>
+    </xsl:copy>
+  </xsl:template>
+
+
+  <!-- Copy command and add nodes -->
+  <xsl:template match="vty:command">
+    <xsl:copy>
+      <xsl:apply-templates select="@*|node()" />
+      <xsl:variable name="info" select="document($with)/vty:vtydoc/vty:node[@id=current()/../@id]/vty:command[@id=current()/@id]/." />
+      <xsl:for-each select="$info/*">
+          <xsl:copy-of select="." />
+      </xsl:for-each>
+    </xsl:copy>
+  </xsl:template>
+</xsl:transform>
+
diff --git a/doc/vty/vtydoc.xsd b/doc/vty/vtydoc.xsd
new file mode 100644
index 0000000..53a67a3
--- /dev/null
+++ b/doc/vty/vtydoc.xsd
@@ -0,0 +1,46 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<xs:schema
+    xmlns="urn:osmocom:xml:libosmocore:vty:doc:1.0"
+    xmlns:xs="http://www.w3.org/2001/XMLSchema"
+    targetNamespace="urn:osmocom:xml:libosmocore:vty:doc:1.0"
+    elementFormDefault="qualified"
+    attributeFormDefault="unqualified">
+
+    <xs:complexType name="ParamType">
+        <xs:attribute name="name" type="xs:string" use="required" />
+        <xs:attribute name="doc" type="xs:string" use="required" />
+    </xs:complexType>
+
+    <xs:complexType name="ParamsType">
+        <xs:sequence>
+            <xs:element name="param" type="ParamType" maxOccurs="unbounded" />
+        </xs:sequence>
+    </xs:complexType>
+
+    <xs:complexType name="CommandType">
+        <xs:sequence>
+            <xs:element name="doc" type="xs:string" minOccurs="0" maxOccurs="1" />
+            <xs:element name="params" type="ParamsType" minOccurs="1" maxOccurs="1"/>
+            <xs:element name="enter" type="xs:string" minOccurs="0" maxOccurs="unbounded" />
+        </xs:sequence>
+        <xs:attribute name="id" type="xs:string" use="required" />
+    </xs:complexType>
+
+    <xs:complexType name="NodeType">
+	<xs:sequence>
+		<xs:element name="command" type="CommandType" minOccurs="0" maxOccurs="unbounded"/>
+	</xs:sequence>
+        <xs:attribute name="id" type="xs:anyURI"/>
+        <xs:attribute name="name" type="xs:string"/>
+    </xs:complexType>
+
+    <!-- the main entry -->
+    <xs:element name="vtydoc">
+        <xs:complexType>
+            <xs:sequence>
+                <xs:element name="node" type="NodeType" minOccurs="0" maxOccurs="unbounded"/>
+            </xs:sequence>
+        </xs:complexType>
+    </xs:element>
+</xs:schema>
+